J. Biol. Chem., Vol. 261, Issue 26, 12159-12165, 09, 1986
Conformational control of ovoperoxidase catalysis in the sea urchin fertilization membrane
TL Deits and BM Shapiro
The ovoperoxidase-catalyzed oxidation of iodide has been investigated as a
function of pH for the homogeneous enzyme and for ovoperoxidase
incorporated into several forms of the egg fertilization membrane. The pH
dependent hysteresis previously observed in purified ovoperoxidase (Deits,
T. L., Shapiro, B. M. (1985) J. Biol. Chem. 260, 7882-7888) is entirely
absent in ovoperoxidase incorporated into the mature fertilization
membrane, where the enzyme is bound noncovalently in vivo. The pH activity
profile of ovoperoxidase incorporated into the mature fertilization
membrane closely resembles the profile observed only transiently in
purified ovoperoxidase subjected to a rapid downward pH shift. These
observations can be accounted for by our previously presented mechanism for
ovoperoxidase hysteresis (ibid.). We hypothesize that ovoperoxidase, upon
incorporation into the fertilization membrane, is restricted to a limited
subset of the conformational states available to the purified enzyme. This
matrix- dependent conformational restriction is a novel control mechanism
that serves to enhance the catalytic activity of ovoperoxidase upon its
assembly into the fertilization membrane and thereby modulates
ovoperoxidase catalysis in the vicinity of the developing egg.