Enzyme kinetics

Enzyme kinetics - C H A P T E R 8 ENZYME KINETICS S, P, and...

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95 C H A P T E R 8 ENZYME KINETICS S, P, and E (Substrate, Product, Enzyme) Amounts and Concentrations Active Site Assay Velocity Initial Velocity Mechanism Little k ’s Michaelis-Menten Equation V max k cat K m Special Points k cat / K m Rate Accelerations Steady-State Approximation Transformations and Graphs Inhibition Allosterism and Cooperativity The Monod-Wyman-Changeaux Model
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96 Basic Concepts in Biochemistry Kinetics seems scary, but understanding just a few things spells relief. Two problems with kinetics are the screwy (and often unexplained) units and the concepts of rate and rate constant . And you can’t ignore enzyme kinetics; it forms the foundation of metabolic regulation, provides a diag- nostic measure of tissue damage, and lies at the heart of drug design and therapy. The most well-studied enzyme catalyzes the reaction S s P. The kinetic question is how time influences the amount of S and P. In the absence of enzyme, the conversion of S to P is slow and uncontrolled. In the presence of a specific enzyme (S-to-Pase 1 ), S is converted swiftly and specifically to product. S-to-Pase is specific; it will not convert A to B or X to Y. Enzymes also provide a rate acceleration. If you compare the rate of a chemical reaction in solution with the rate of the same reaction with the reactants bound to the enzyme, the enzyme reaction will occur up to 10 14 times faster. AMOUNTS AND CONCENTRATIONS AMOUNT CONCENTRATION A quantity A quantity/volume mg, mole M (mol/L), m M g, m mol m M , mg/mL units units/mL Quantities such as milligrams (mg), micromoles ( m mol), and units refer to amounts. Concentration is the amount per volume, so that molar ( M ), micromolar ( m M ), milligrams per milliliter (mg/ml), and units per milliliter (units/ml) are concentrations. A unit is the amount of enzyme that will catalyze the conversion of 1 m mol of substrate to product in 1 min under a given set of conditions. S, P, AND E (SUBSTRATE, PRODUCT, ENZYME) Enzyme (E) converts substrate(s) (S) to product(s) (P) and acceler- ates the rate. 1 Enzymes are named by a systematic set of rules that nobody follows. The only given is that enzyme names end in -ase and may have something in them that may say something about the type of reaction they catalyze—such as chymotrypsin, pepsin, and enterokinase (all proteases).
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8 Enzyme Kinetics 97 The concentrations of substrate and product are invariably in molar units ( M ; this includes m M , m M , etc.), but enzyme concentrations may be given in molar ( M ), milligrams per milliliter (mg/mL), or units/mL. The amount of enzyme you have can be expressed in molecules, mil- ligrams, nanomoles (nmol), or units. A unit of enzyme is the amount of enzyme that will catalyze the formation of 1 m mol of product per minute under specifically defined conditions. A unit is an amount, not a con- centration.
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This note was uploaded on 04/09/2008 for the course BIO SCI 98 taught by Professor Goulding during the Spring '08 term at UC Irvine.

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Enzyme kinetics - C H A P T E R 8 ENZYME KINETICS S, P, and...

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