Biochem Ch. 7 Enzyme Kinetics & Regulation

first-order reaction

the velocity of a reaction is directly proportional to reactant concentration V=k[A]

second-order reaction

rate depends on two reactants colliding, doubling would equal in 4x speed (ex: dance floor where two people collide) V=k[A]² or V=k[A][B]

initial velocity (Vo)

the early reaction rate measured before substrate drops or product accumulates—giving the purest snapshot of enzyme activity

KM

= k-1+k₂ / k₁

What does KM indicate?

the substrate binding with the enzyme

a high KM

low binding

a low KM

high binding

dissociation constant

the concentration of ligand needed to occupy half of the binding sites, and it directly reflects how tightly two molecules bind (ex: how tightly you hold a balloon and how often it gets away)

turnover number

K2 or kcat, the number of substrate molecules converted into product per second

Michaelis-Menten equation

Vmax (kcat)

top speed of the enzyme, can’t work any faster

Lineweaver-Burk equation

double-reciprocal equation, turns curved Michaelis-Menten graph into a straight line

allosteric control

a molecule binds to a site on an enzyme other than the active site and changes the enzyme’s activity

aspartate transcarboxylase (ATCase)

catalyzes the first step in pyrimidine synthesis

feedback inhibition

ATCase is inhibited by the end product of the pathway, CTP

How are allosterically regulated enzymes different kinetically?

sigmoidal curve

threshold effect

small change in substrate concentration has significant impact

How are allosteric interactions in ATCase mediated?

by large changes in quaternary structure

What are the parts of a catalytic trimer?

regulatory / r chain, catalytic / c chain, and regulatory dimer

ATCase T-state

lowers enzyme activity, favored by CTP binding

ATCase R-state

more relaxed, opens up, favored by substrate binding