Abstract
The proteolytic activity in the digestive system of the silkworm was measured by determing of U. V. absorption and the ninhydrin reaction. When the substrate was incubated with digestive fluid at pH 11.2, O. D. at 280nm was increased very rapidly, whereas the amount of ninhydrin positive substances reached 10% of complete hydrolysis of substrate and maintained this level. Subsequently, the product by protease of digestive fluid was incubated with midgut enzyme preparation at pH 6.85. The ninhydrin positive substances were increased markedly. Furthermore, the peptides produced by protease of the digestive fluid were separated by means of gel filtration on Sephadex column and their molecular weight was estimated to be about from 600 to 4, 000. These results indicate that there is a functional differentiation between digestive fluid and midgut tissue concerning the protein hydrolysis in the silkworm : High molecular proteins are hydrolyzed into peptides in digestive fluid at strong alkaline condition, and the peptides absorbed in the tissue were hydrolyzed into amino acids by the midgut peptidases.
