Abstract
When cytoplasmic polyhedra from the silkworm, Bombyx mori, were dissolved in alkaline condition, the polyhedron matrix protein, which has a molecular weight of 30, 000, was degraded into low molecular weight components as well as cases from some baculoviruses and entomopoxvirus. The quantity of the several degraded components depended on the duration of the dissolution in alkaline condition. To determine whether its degradation is due to the occurrence of alkaline protease in cytoplasmic polyhedra or not, protease activity has been measured by release of amino acids and oligopeptides from casein as a substrate. This degradation occured at pH 11.0 markedly, and 40°C was an optimum temperature. It was heat labile, i.e., 95% of the activity was destroyed by heating at 50°C for 15 min, and mercuric ion. From these results it has been confirmed that the cleavage of polyhedron protein is due to alkaline protease.
