Results of kinetic studies on dissociative thermal inactivation of oli
gomeric enzymes are discussed. Dissociative thermal inactivation is th
e process in which the kinetically irreversible protein change is prec
eded by a reversible stage of oligomer dissociation. In experiments, t
his is demonstrated by the dependence of inactivation rate on total pr
otein concentration. This paper gives the relations which allow the ca
lculation from experimental data the following physicochemical constan
ts which characterize the stability of oligomeric enzymes: the constan
t for the rate of irreversible change of monomeric protein, the equili
brium constant for dimer dissociation, and the tate constant for dimer
dissociation. The problem of a ''conformational lock'', the contact b
etween protein globules that admits a multistep destruction of active
oligomer and explains the induction period occurring in kinetic therma
l inactivation curves, is discussed. The X-ray structural analyses for
several dimeric enzymes, i.e., alkaline phosphatase (EC 3.1.3.1) from
E. coli, alcohol dehydrogenase (EC 1.1.1.1) from horse liver, and bak
er's yeast enolase (EC 4.2.1.11), explain why they lose catalytic acti
vity during the dissociation of the protein into monomers and also pro
vide a physically reasonable picture of the structure of their conform
ational lock. Also, these data support the kinetic scheme used to desc
ribe the dissociative inactivation of dimeric enzymes.