Neurochemistry 12011 Tim Murphy

Objective: To understand the metabolic processes underlying the synthesis

and metabolism of amino acid and peptide neurotransmitters.

Major points to be covered:

-regulation of metabolism by enzymes

-metabolic processes neurons share with other cells and organs

-properties and functions of enzymes and pumps (transporters).

-metabolic contingencies imposed by the existence of a blood-brain-

barrier, i.e. the central role of glucose

-synthesis and metabolism of amino acid transmitters and GABA.

-glutamate

-aspartate

-glycine

-neuropeptide synthesis and the pathway to regulated release

*

Neuronal metabolism.

Neurons share with other cells the need and ability to synthesize nucleic acids, proteins, carbohydrates and lipids.Likewise they share the metabolic processes required to generate chemical energy for these processes: glycolysis, pentose-phosphate shunt, citric acid cycle, oxidative phosphorylation.Neurons must be able to synthesize and metabolize neurotransmitters.Neurons must also synthesize second messenger molecules needed to mediate signal transduction.

The brain makes use

of general metabolism

to find precursors

and in some cases the

finished products for

synaptic physiology.

glycine

Enzymes

Help processes within neurons overcome activation energy, and provide a site of regulation.Essentially all chemical reactions in cells are mediated by enzyme, protein catalysts.A catalyst acts by bringing together the reactants, and thereby increasing the rate of a chemical reaction, without being permanently changed in the reaction.Enzymes also allow the coupling of energetically unfavourable reactions with reactions that release free energy. If together the two reactions result in a negative G, the coupled reaction can occur.

Enzymes lower

activation energy

for reactions.

Mol. Biol. of the Cell

Enzymes permit coupled reactions, for example falling rocks

turn wheel to raise water for a different type of work.

Mol. Biol. of the Cell

ATP is a useful energy currency

since it can form high-energy

intermediates permitting

the coupling of energetically

unfavorable reactions to favorable

ones, shown is the amination

of glutamate.

Mol. Biol. of the Cell

General Properties of Enzymes

Enzymes are highly specific due to the specific structure of the active siteSubstrate specificityReaction specificityEnzymes bind substrates in specific ways that stabilize a reactive conformation, known as the TRANSITION STATESome enzymes require cofactors for complete activity (vitamin B6, pyridoxyl deficiency can impact GABA synthesis).

Velocity (V) as a function of substrate (S) plot.

Km

Saturation

pseudo

1st order

V=Vmax* [S]/([S]+Km)

With a competitive inhibitor, the Km is increased but

the Vmax is not effected.

Km=Km*(1+[I]/Ki), note when I= Ki the Km doubles

With a noncompetitive inhibitor only the Vmax is reduced.

Vmax=Vmax*(1-[I]/([I]+Ki)), note when I= Ki the Vmax halves

Michaelis-Menton Equation, describes saturable enzyme kinetics,

also applicable to binding of ligands to receptors.

know this, it describes many

interactions: enzymes, receptors,

protein-protein.

Km and Vmax

The activity of enzymes can be discussed in terms of their Km, a measure of the affinity of the enzyme for its substrate, and the Vmax, which is the maximal velocity of the enzymatic reaction.Km has two meanings: 1) the concentration of substrate at which 1/2 the active sites on an enzyme are filled. 2) the ratio of dissociation to association rates for enzyme substrate interactions. Km=kdissoc/kassoc. Since the association rates of many reactions at going the speed of diffusion, the strength of binding and rates of reaction are often determined by the dissociation rate. Although these terms are associated with enzymes they are related to other saturable systems such as transporters (Kt, Vmax) and receptors (Kd, Bmax).

Competitive inhibitors.

Action: at the catalytic site, where it competes with substrate for binding in a dynamic equilibrium- like process. Inhibition is reversible by substrate. Effect: Vmax is unchanged; Km, as defined by [S] required for 1/2 maximal activity, is increased.

Noncompetitive inhibitors.

Action:Binds E or ES complex other than at the catalytic site. Substrate binding unaltered, but ESI complex cannot form products. Inhibition cannot be reversed by substrate. . Effect: Vmax is reduced; Km, as defined by [S] required for 1/2 maximal activity, is unchanged. Knowing if something is competitive or non-competitive is important since it determines how much inhibitor you need relative to substrate (practical implication!!)

Substrate or ligand concentration

Chart2

0.16666666670.09090909090.0833333333

0.50.33333333330.25

0.64285714290.47368421050.3214285714

0.72222222220.56521739130.3611111111

0.77272727270.62962962960.3863636364

0.80769230770.67741935480.4038461538

0.83333333330.71428571430.4166666667

0.85294117650.74358974360.4264705882

0.86842105260.76744186050.4342105263

0.8809523810.78723404260.4404761905

0.89130434780.80392156860.4456521739

0.90.81818181820.45

0.90740740740.83050847460.4537037037

0.91379310340.84126984130.4568965517

0.91935483870.85074626870.4596774194

0.92424242420.85915492960.4621212121

0.92857142860.86666666670.4642857143

0.93243243240.87341772150.4662162162

0.93589743590.87951807230.4679487179

0.93902439020.88505747130.4695121951

0.94186046510.89010989010.4709302326

0.94444444440.89473684210.4722222222

0.94680851060.8989898990.4734042553

0.94897959180.90291262140.4744897959

0.95098039220.90654205610.4754901961

0.95283018870.90990990990.4764150943

0.95454545450.91304347830.4772727273

0.95614035090.91596638660.4780701754

0.95762711860.9186991870.4788135593

0.95901639340.92125984250.4795081967

0.96031746030.92366412210.4801587302

0.96153846150.92592592590.4807692308

0.96268656720.9280575540.4813432836

0.96376811590.93006993010.481884058

0.96478873240.93197278910.4823943662

0.96575342470.93377483440.4828767123

0.96666666670.9354838710.4833333333

0.96753246750.93710691820.4837662338

0.96835443040.93865030670.4841772152

0.96913580250.94011976050.4845679012

0.96987951810.94152046780.484939759

0.97058823530.94285714290.4852941176

0.97126436780.94413407820.4856321839

0.97191011240.94535519130.4859550562

0.97252747250.94652406420.4862637363

0.97311827960.94764397910.4865591398

0.97368421050.94871794870.4868421053

0.97422680410.94974874370.4871134021

0.97474747470.95073891630.4873737374

0.97524752480.95169082130.4876237624

0.97572815530.95260663510.4878640777

V control

V comp. Inh.

V noncomp. Inh.

substrate or ligand [ ]

velocity or binding

Receptor binding or enzyme Vel.

Sheet1

[S]V controlV comp. Inh.V noncomp. Inh.VmaxKmKiI

10.16666666670.03225806450.02777777781515

50.50.14285714290.0833333333change above values see graph

90.64285714290.23076923080.1071428571

130.72222222220.30232558140.1203703704

170.77272727270.36170212770.1287878788

210.80769230770.41176470590.1346153846don't change values

250.83333333330.45454545450.1388888889below calculated from formulas

290.85294117650.49152542370.1421568627Km comp

330.86842105260.52380952380.144736842130

370.8809523810.5522388060.1468253968Vmax comp.

410.89130434780.57746478870.14855072461

450.90.60.15Vmax non comp.

490.90740740740.62025316460.15123456790.1666666667

530.91379310340.63855421690.1522988506Km noncomp.

570.91935483870.65517241380.15322580655

610.92424242420.67032967030.154040404

650.92857142860.68421052630.1547619048

690.93243243240.6969696970.1554054054

730.93589743590.70873786410.155982906

770.93902439020.71962616820.156504065

810.94186046510.72972972970.1569767442

850.94444444440.73913043480.1574074074

890.94680851060.74789915970.1578014184

930.94897959180.7560975610.1581632653

970.95098039220.76377952760.158496732

1010.95283018870.77099236640.1588050314

1050.95454545450.77777777780.1590909091

1090.95614035090.78417266190.1593567251

1130.95762711860.79020979020.1596045198

1170.95901639340.79591836730.1598360656

1210.96031746030.80132450330.1600529101

1250.96153846150.80645161290.1602564103

1290.96268656720.81132075470.1604477612

1330.96376811590.81595092020.1606280193

1370.96478873240.82035928140.1607981221

1410.96575342470.82456140350.1609589041

1450.96666666670.82857142860.1611111111

1490.96753246750.83240223460.1612554113

1530.96835443040.83606557380.1613924051

1570.96913580250.83957219250.1615226337

1610.96987951810.84293193720.1616465863

1650.97058823530.84615384620.1617647059

1690.97126436780.84924623120.1618773946

1730.97191011240.85221674880.1619850187

1770.97252747250.85507246380.1620879121

1810.97311827960.85781990520.1621863799

1850.97368421050.86046511630.1622807018

1890.97422680410.86301369860.162371134

1930.97474747470.8654708520.1624579125

1970.97524752480.86784140970.1625412541

2010.97572815530.87012987010.1626213592

Sheet1

V control

V comp. Inh.

V noncomp. Inh.

substrate or ligand [ ]

velocity or binding

Receptor binding or enzyme Vel.

Sheet2

Sheet3

Transport can

be saturable.

*

Relative

scales, simple

diffusion rates

will be low for

polar substances.

*

Channels and carriers.

*

*

Since many transported compounds are charged their movement is governed by electrical and chemical gradients just like small ions such as K+, Na+, Cl-, and Ca2+.

*

Uniports-facilitative or uncoupled transport

Molecules or ions move down their concentration gradient via a specific carrier.In contrast to a channel which will allow movement of thousands of ions per millisecond and whose specificity is primarily mediated by pore size, a facilitative carrier requires binding of a specific substrate which induces conformational changes in the carrier through which the substrate is moved, and then released, restoring the carrier to its original conformation.

Carrier-Mediated Transport, Uniporters.

Carrier types at the blood brain barrier: hexose, monocarboxylic acid, large neutral amino acid, basic amino acid, acidic amino acid, choline, purine, and nucleoside carriers.These substances serve as building blocks for all brain macromolecules and neurochemicals.

*

Symports and antiports

Couple movement of one molecule with that of one or more other substrates. Energy is derived from concentration gradients no ATP needed (directly) although indirectly to establish gradient.The high-affinity pumps for amino acids, and neurotransmitters are principally Na+-symporters, i.e. the movement of Na+ down its electrochemical gradient provides the free-energy required to move another substrate (neurotransmitter) up its concentration gradientNa+/Ca++ antiporters, and Na+/H+ antiporters move these ions out of cells as Na+ enters.

Na+, Ca2+

exchange

Glutamate

protons

*

The Na+ gradient can be used

to pump glucose uphill.

*

*

Primary active transport

Systems utilize the free-energy obtained by ATP hydrolysis to move ions against concentration gradients (uphill), i.e. Na+-, K+-ATPase or the Ca2+ ATPase.Estimated to require up to half the brain ATP, while other biochemical processes including protein, lipid and neurotransmitter synthesis together use perhaps 10%. Other primary pumps, such as Ca2+-ATPases and proton pumps probably account for the rest. The brain uses 20% of total body oxygen consumption, thus 10% of total is used primarily to maintain neuronal ionic gradients via this pump.

Na+, K+ ATPase

*

Na+, K+ ATPase

Energy is directed into the pumping process by the 3Na+-dependent phosphorylation, followed by the 2K+-dependent dephosphorylation. Phosphorylation induces a conformational change that moves 3Na+ to the outside of the cell.Pump stoichiometry is 3/2 making it electrogenic.

Fundamental Neurosci.

2002 Zigmond et al.

Role of the pump in resting membrane potential.

If pump is blocked with ouabain (blocks binding of K+) an immediate small depolarization occurs (only a few mV), however membrane will remain relatively constant as it is largely determined by K+ permeability, however the membrane is also slightly permeable to Na+ and over time the membrane potential will depolarize if Na+ diffuses in unchecked by the pump.

Glucose

Is the major fuel of the brain because it is the only fuel which enters in sufficient amounts to support the energy requirements.Glucose gains access to brain and into cells by specific carriers - blood levels much higher than brain levels, thus glucose moves down its concentration gradient via facilitative transport.Glucose utilization of tied to neuronal activity and increased blood flow, basis of PET functional imaging with 2-deoxyglucose.Isolated neurons can use other fuels such as pyruvate and lactate, but they normally are not BBB permeable.

Blood

(~6 mM

glucose).

4X Glut-1

expressed on the

ab-lumenal side

Farrell and Pardridge

1991

CSF

(~4 mM

glucose).

Fundamental Neurosci. 2002 Zigmond et al.

Glucose transport

The Km of the BBB glucose transporter is about 7 mM, which is about the level of plasma glucose, thus brain glucose varies directly with changes in blood levels. The blood brain barrier transporter is Glut-1.Neurons possess a carrier of higher affinity, Glut3 Km = 200 M, allowing them to extract glucose from the extracellular space. Within neurons, glucose is immediately phosphorylated to a charged, impermeant metabolite, glucose-6-phosphate, thus the intracellular glucose concentration is effectively zero. Why is it advantageous to reduce the apparent free concentration of glucose.

Used in

PET scanning.

Fundamental Neurosci.

2002 Zigmond et al.

Glycolysis and TCA cycle

Within the cell, glucose enters the glycolysis pathway in the cytoplasm, and via pyruvate and acetyl-CoA, in the mitochondrial tri-carboxylic acid cycle (TCA) or Krebs cycle. In these systems, reducing equivalents are generated and via oxidative phosphorylation they generate ATP, the chemical fuel for the brain.Glycolysis and the TCA cycle are also the source of non-essential amino acid precursors used to synthesize the neurotransmitters glutamate, aspartate, GABA, and glycine.

Blood brain barrier.

What is the blood brain barrier (BBB)?The existence of a blood-brain-barrier prevents molecules in the circulation from freely entering the brain.Prevents constant fluctuations in circulating metabolites, ions, and hormones from directly influencing neuronal activity.Diffusion allows passage of gases, i.e. (O2 and CO2) and lipid soluble compounds, i.e. psychoactive drugs.

The blood brain

barrier largely occurs

at capillaries through

astrocyte endfeet and

endothelium tight junctions.

Transport across it is selective. Carrier types at the blood brain barrier: hexose,monocarboxylic acid, large neutral amino acid, basic amino acid, acidic amino acid, choline, purine, and nucleoside carriers. Drewes LR. Adv Exp Med Biol. 1999;474:111-22.

.

Endothelium

Iadecola and Nedergaard 2007 Nat. Neurosci.

Perivascular glia contain high

levels of the antioxidant tripeptide glutathione Sun et al. 2006.

Paulson, European Neuropsychopharmacology

12, 2002, Pg. 495

Fig. 1. Characteristics of the endothelium. In the muscle capillary (upper) there are pores or slits between the endothelial cells allowing bulk flow of water and smaller solutes between the blood and the extracellular space in the tissue. In contrast, the brain endothelial cells (lower) are connected by tight junctions. No pores or slits are present preventing bulk flow. Water therefore has to cross the bloodbrain barrier by the mechanism of diffusion.

Brain activity and blood supply are tightly linked.

It has been known for over 100 years increased neuronal activity is associated with increases in blood flow. Roy CS, Sherrington CS (January 1890). "On the Regulation of the Blood-supply of the Brain". J. of Physiol. 11 (1-2): 85158.17.Changes in blood flow or oxygenation are used a surrogate measure of neuronal activity.

Glial and neuronal control of brain blood flow David Attwell1, Alastair M. Buchan2, Serge Charpak3, Martin Lauritzen4, Brian A. MacVicar5 & Eric A. Newman6 Nature 2010 468:231

Glial and neuronal control of brain blood flow

Imaging brain metabolism.

2-deoxygluocose method radioactive detection or positron emission tomography (PET) scanning, need isotopes poor time resolution (Sokoloff 1977 J. of Neurochem.).Functional magnetic resonance imaging (fMRI), second level time resolution, signals related to changes in oxy/deoxyhemoglobin potentially complicated (Ogawa et al. 1990 PNAS).Intrinsic signal imaging more direct spectroscopy of brain signals related to changes in oxy/deoxyhemoglobin, can be performed with a video camera (Grinvald et al. 1986 Nature).

10 mm

Synapses are on average 13 mm from capillaries. RBC supply rates are normally ~100 cells/sec.

Acute reduction in supply

rate by >90% leads to damage within 10 min,

which can reverse if reperfusion occurs early.

Zhang et al. 2005

Scale bar=10 um

region1 ctr at 49_54

10 mm

Control 10 min 30 min

1 hr 2 hr 3 hr

Irreversible ischemia; red vessels, green dendrites (Murphy lab).

clot

635 nm light

1) Reduced reflection, increased absorbance with elevated

deoxyhemoglobin in active areas.

2) General increase in blood volume and oxyhemoglobin in surrounding areas leads to large late positive global signal.

Intrinsic optical signals, light scattering provides

a reflection of neuronal activity.

Stim 1 sec

Reflected light

2) General blood

volume.

Local deoxyhemo-

globin signal.

From Grinvald and Bonhoeffer

OPTICAL IMAGING OF ELECTRICAL ACTIVITY BASED ON INTRINSIC SIGNALS AND ON VOLTAGE SENSITIVE DYES THE METHODOLOGY 2001

Sources of intrinsic optical signals.

Change in light scattering in

response to forelimb stimulation.

Neurotransmitters:

small molecule and neuropeptide.

Small molecule

Neurotransmitters (MW

Neurotransmitter transporters:

Plasma membrane forms terminate neurotransmission, replenish neurotransmitter pool, and may have a signaling function.Vesicular transporters use both concentration gradient and protons to concentrate transmitter in vesicles: these transporters make neurons transmitter specific.

Molecular structure of plasma memb. neurotransmitter transporters:

Norepinephrine, GABA, serotonin, dopamine, glycine, choline, and proline transporters Homologous in their 12 transmembrane spanning domains.In the case of GABA, transport results from the co-transport of Na+ and Cl- ions

Glutamate plasma memb. transporters form a distinct family.

Structure different from other transmitter transporters-8 transmembrane domains not related to other existing mammalian transporter clones.Homologous to each other (~50%) and to a bacterial proton-coupled glutamate transporter.Glast1 (EAAT1), Storck et al. PNAS 89, 10955-10959 (1992). Expressed in glial cells.GLT-1 (EAAT2), Pines et al. Nature 360, 464-467 (1992). Localized to glial cellsEAAC1 (EAAT3), Kanai and Hediger Nature 360, 467-471 (1992). Relatively neuron specific in brain, also expressed in intestinal tissues, and kidney.

Transporter is electrogenic allowing its current to be measured and studied with the patch clamp method.

Vesicle glutamate transporters.

Several members including VGLUT1 and VGLUT2, and VGLUT3 isolated by R. Edwards lab (Science;289:957-60, 2000 first publication). Defines glutamatergic neuron classes, although all neurons contain glutamate, only those expressing VGLUTs can package it at high concentrations for synaptic release.Transport mediated by a combination of H+ and ionic gradients.

Chaudhry et al. 2002 JCB.

Vesicular accumulation

of amino acids results from

both a gradient of membrane

potential and pH.

Neurotransmitter glycine.

Non-essential amino acid derived from glycolysis and TCA cycle intermediates.Glycine made from glucose via amino acid serine.High-affinity uptake system removes glycine from synapse. Shares a vesicular pump with GABA, VGATGlycine and its pump found in high levels in spinal cord, in neurons presynaptic to strychnine-sensitive glycine receptor-chloride channel.Receptors mainly found in the spinal cord.

Neurotransmitter glutamate

Na+-dependent, high-affinity uptake system has been well characterized, and occurs principally in glutamate nerve terminals (EAAC-1/EAAT3).Glutamate uptake into glial cells allows metabolism via glutamine synthetase. Glutamine formed in glia then enters neurons to provide a precursor for glutamate synthesis via glutaminase activity. Since glutamate transport is determined by ion concentration gradients it is described by the Nernst potential. At positive voltages the transporter can reverse (may occur during a stroke).

Astro Gln efflux

through system N.

Neuronal Gln uptake by system A.

see Chaudhry et al.

2002 JCB.

Fundamental Neurosci.

2002 Zigmond et al.

Fundamental Neurosci.

2002 Zigmond et al.

Fundamental Neurosci.

2002 Zigmond et al.

Reference only, Glutamate metabolism, 4 possible synthetic pathways

1) From -ketoglutarate (2-oxoglutarate) and ammonia via glutamate dehydrogenase. This pathway is of fundamental importance in the synthesis of all amino acids, since it is the key mechanism for the formation of -amino groups directly from ammonia. Transamination of -keto acids with glutamate as amino group donor then allows the introduction of -amino groups into the synthesis of other amino acids.

2) From -ketoglutarate and aspartate by aspartate aminotransferase; antibodies to this enzyme stain many presumed glutamate neurons

3) From glutamine by glutaminase; antibodies to this enzyme also stain some presumed glutamate neurons. Glutaminase removes the NH2 from the glutamine.

4) From -ketoglutarate by ornithine-aminotransferase or via proline oxidase. Both these pathways form P5C (pyroline 5-carboxylic acid), which via P5C dehydrogenase can yield glutamate. There is no evidence yet that these are neuronal enzymes. However, a high-affinity proline uptake system has recently been found that appears to be associated with glutamate pathways.

(astrocyte)

Fundamental Neurosci.

2002 Zigmond et al.

Neuropeptide neurotransmitters.

History i.e. regulated release of enzymes from exocrine cells, and hormones such as insulin from endocrine cellsThe discovery of vasopressin release from posterior pituitary in the 1940s by du Vigneaud demonstrated that neurons could secrete peptides for intercellular communicationThis was followed by the discovery of hypothalamic factors regulating the anterior pituitary by Guillemin and SchallyThe discovery, in the mid-seventies, of enkephalins as endogenous ligands for discovered opiate receptors.

Fundamental Neurosci.

2002 Zigmond et al.

Synthesis and processing of neuropeptides, RNA.

mRNA splicing to generate different bioactive peptides, selective usage of some exons. A mechansim by which a single gene encodes polypeptides of varied function. Splicing occurs in the nucleus. Substance P and substance K are encoded by the same gene but are only found together in mature mRNA in some tissues. Calcitonin and CGRP are formed in different neurons by alternative splicing of introns.mRNA moves through nuclear pores and into cytoplasm.

Peptide synthesis.

Proteolytic maturation then occurs in acidic, clathrin-coated secretory vesicles. Involves endopeptidases, which often cleave C-terminal to the paired dibasic amino acids, i.e. Lys-Arg, Arg-Arg. POMC can be processed into at least 6 different peptide hormones through proteolytic cleavage (ACTH, bendorphin, Clip, aMSH, gMSH, bLPH, etc). Processing can be specific to different brain or pituitary regions.The dibasic residues are then removed by carboxypeptidase.

Peptide synthesis.

Some prohormones, i.e. somatostatin, are cleaved by other endopeptidases, N-terminal to dibasic pairs, which are then removed by aminopeptidases.Many peptides end in a modified C-terminal amide. This is formed by the action of peptidyl-glycine--amidating monooxygenase (PAM) which converts the C terminal Gly to a amide group. Amidation is critical for the function of some peptides (such as substance P).Vesicles containing peptides are moved via fast axonal transport to release sites

Degradation

specific uptake systems have not been identifiedpresumably, diffusion from synapses, and proteases of various sorts on the surface of neurons and glia cleave the peptides to their constitutive amino acids, which can then be reutilized

Methods of study

Purification via bioassay, chemical assay, molecular cloningSynthesis allows antibody production, RIA, immunohistochemistry, radioligand binding, electrophysiologyMost peptides act via G protein-coupled receptors modulate K+ channels and Ca++ channels and can be studied electrophysiologically.

Anatomy, localization

Found in most, if not all neurons, can coexist with other peptides or with amine and amino acid transmitters, present in dense core large vesicles.Made in the cell body on ribosomes and transported to terminals.If a prohormone is cleaved prior to packaging in vesicles, it is possible to sort the mature peptides to different vesicles. In fact, work in Aplysia indicates that peptides in distinct vesicles can be sorted to different neuronal compartments Cell, 54:813-822 1988. This would appear to contravene Dales Law: 1) a neuron has only one transmitter and 2) a neuron is only excitatory or inhibitory.

Readings

Fundamental Neuroscience Fundamental Neuroscience 1st Ed., Chapter 8, p. 193-234 Chapter 14, p.389-392. Or 2nd Ed. Chapter 7 p. 167-196 and Chapter 13 339-360. In 3rd Edition Chap. 7 starting pg.133 and Chapter 12 starting pg. 271.Cooper, Bloom & Roth, The Biochemical Basis of Neuropharmacology, Chaps. 7-13, 6th Ed or Chaps 6-11 7th Ed.Molecular Biology of the Cell 4th ed. Chapter 11 or Molecular Biology of the Cell 3rd ed. Chapter 11 p 507-523.

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170.7727270.3617021280.128787879

210.8076920.4117647060.134615385

250.8333330.4545454550.138888889

290.8529410.4915254240.142156863

330.8684210.5238095240.144736842

370.8809520.5522388060.146825397

410.8913040.5774647890.148550725

450.90.60.15

490.9074070.6202531650.151234568

530.9137930.6385542170.152298851

570.9193550.6551724140.153225806

610.9242420.670329670.154040404

650.9285710.6842105260.154761905

690.9324320.6969696970.155405405

730.9358970.7087378640.155982906

770.9390240.7196261680.156504065

810.941860.729729730.156976744

Receptor binding or enzyme Vel.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

[S]21456993117141165189

substrate or ligand [ ]

velocity or binding

V control

V comp. Inh.

V noncomp. Inh.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

99.90

99.95

100.00

100.05

100.10

100.15

100.20

reflected 635 nm light

Time (sec)