Biochemistry-Chapter 13: Enzymes-Kinetics and Specificity

enzymes

~used to catalyze thermo favored reactions

~control rate and allow for regulation

~features: catalytic power, specificity, and regulation

catalytic power

~relative power = rate calculated reaction/rate of uncatalyzed

~example: hydrolysis of urea by urease

specificity

~enzymes ability to selectively process its substrate

~very selective for substrate

~very selective for reaction

~products are formed in very high yield with minimal biproducts (typically 99% yield_

regulation

activity must be regulated to meet cellular needs

nomenclature

~traditionally, enzymes have been named by adding -ase to substrate name (ex: urease)

~to avoid confusion, a systematic naming has been developed

~all enzymes are assigned to one of six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases

~within each class are subclassifications and subclasses of subclasses

~non-protein components which allow for enzyme activity

oxidoreductase enzymes

relate to oxidation-reduction reactions

transferases

transfer of a functional group

hydrolases

results in hydrolysis reaction

lyases

bond breaking enzyme by means other than redox or hydrolysis

isomerases

isomerization reactions

ligases

bond formation by using ATP as energy source

cofactors

~metal ions or small organic molecules (coenzymes)

~ex: vitamins

prosthetic groups

very tightly held cofactors

apoenzyme

just the protein with no bound cofactors

holoenzyme

protein + all coenzymes and cofactors

enzyme kinetics

~determine the maximum (velocity rate) for an enzyme under specific conditions

~determine the binding affinity of the substrate

~fundamental kinetics (A --> P so rate = delta [P]/delta T = -delta[A]/ delta T so rate = k [A]

two ways to increase rate of reaction

~temperature increase (impractical for living systems)

~use a catalyst (lowers Ea but is not consumed; concentration of [A] has no effect on rate [saturated kinetics])