Association-dissociation Properties of NaBH₄-reduced Phosphorylase b

Abstract

Molecular weight studies show that rabbit muscle glycogen phosphorylase is composed of monomeric units with a weight of 9.25 − 10 × 10⁴ daltons (1,2). The enzyme exists as dimers and tetramers, and it has been shown that both phosphorylase b and a undergo dissociation-association reactions which affect enzymic activity (3,4). The formation of the monomer was first demonstrated by Madsen and Cori (5) by reaction of phosphorylase with PMB. Other methods have been used but all of these are rather stringent, and it has not been established whether the monomeric form has catalytic activity. Recent studies with NaBH₄-reduced phosphorylase showed that monomer formation can occur upon enzyme dilution (6). This fact and other studies of its subunit structure (7) led us to study the association-dissociation properties of NaBH₄-reduced phosphorylase* to determine whether the monomeric form of this enzyme is catalytically active.