Factors That Influence Enzymatic Reactions Clinical Chemistry Review 98
FACTOR EXPLANATION OTHER
Substrate concentration
Enzyme concentration
pH
Temperature
Cofactors
Inhibitors
First-order kinetics: [enzyme] > [substrate].
Reaction rate proportional to [substrate].
Zero-order kinetics: [substrate] > [enzyme].
Reaction rate proportional to [enzyme].
Velocity of rxn proportional to [enzyme] as long as
[substrate] > [enzyme].
Extremes of pH may denature enzymes.
Increase of 10ºC doubles rate of rxn until around
40 º–50ºC; then denaturation of enzyme may occur.
Nonprotein molecules that participate in rxn. Must
be present in excess.
Inorganic cofactors (e.g., Cl–, Mg2+) called activa-
tors. Either required for or enhance rxn.
Organic cofactors (e.g., nicotinamide adenine
dinucleotide) called coenzymes. May serve as
2nd substrate in rxn.
Interfere with rxn.
Assays are zero-order (excess substrate).
Unit of measure is international unit (IU). Amount
of enzyme that will catalyze 1 μmol of substrate
per min under standardized conditions.
Most rxn occur at pH 7–8. Use buffers to maintain
optimal pH.
37 °C is most commonly used in U.S.
Rxn commonly used in enzyme determinations:
Nicotinamide adenine dinucleotide (NAD) ¤
nicotinamide adenine dinucleotide, reduced
form (NADH). NADH has absorbance at 340 nm;
NAD does not.
