Effects of anionic steroids and glycolytic intermediates on the catalytic activity, conformation, and stability of phosphorylase B.

Publisher Website
Google Scholar
Abstract
The interaction of anionic steroids with phosphorylase b [from rabbit skeletal muscle] resulted in changes in the binding of pyri-doxal phosphate, as shown by changes in the absorption and fluorescence spectra of the bound cofactor. The pyridoxal phosphate residue in this altered form was more reactive with cysteine and with sodium borohy-dride. The magnitude and rate of the spectral changes were strongly dependent on the presence of various glycolytic intermediates and other compounds recognized as activators, inhibitors, or substrates of the enzyme. Accompanying increases in the reactivity of the enzymic sulfhydryl groups and in the rate of enzyme inactivation were dependent in a similar way on the type of the nonsteroid metabolite in the reaction medium. In ultracentrifuge studies, the distribution of the enzyme between the dimeric and tetrameric forms was also modified by these various nonsteroid effectors. Low levels of the anionic steroids increased the amount of tetramer formed. High levels caused more extensive aggregation. The relevance of these actions to previously reported actions of the anionic steroids and to the function and stability of phosphorylase b in vivo was discussed.

This publication has 15 references indexed in Scilit: