On the interaction of bovine seminal RNase with actin in vitro

Abstract

Ribonuclease from bovine seminal plasma (RNase BS) interacts with skeletal muscle actin in the following way: it (1) binds to actin with an apparent binding constant of 9.2 .times. 104 M-1 in 0.1 M KCl, (2) induces the polymerization of actin below the critical concentration in depolymerization buffer, (3) accelerates the salt-induced polymerization of actin even at a molar ratio of RNase to actin lower than 1/100, and (4) bundles F-actin filaments. In the bundles the molar ratio of RNase to actin is about 0.66. (5) Actin inhibits the enzymatic activity of RNase BS. RNase A from bovine pancreas, which is structurally almost identical to the subunits of RNase BS as well as a monomeric form of RNase BS, do not cross-link actin filaments and have a much smaller effect on the polymerization of actin. We conclude that the dimeric structure of the RNase BS, which consists of two identical subunits cross-linked by interchain disulfide bridges, is probably responsible for the bundling activity and the accelerating effect on the polymerization of actin.