BETA-GLUCOSIDASE OF THE MIDGUT OF THE SILKWORM BOMBYX MORI

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Abstract
1. The presence of a β-glucosidase was demonstrated in the midgut of the silkworm larva, Bombyx mori. 2. The enzyme has a pH optimum of approximately 5.2-6.2 and the Km value was 0.013 with salicin as a substrate. 3. The action of the enzyme was slightly inhibited at a temperature of 40° C., and strongly inhibited at 70° C. An inhibition by silver or mercury salts was also observed, while no inhibition was found by organic acids. No activation by toluene was demonstrated. 4. Most of the activity in the midgut was concentrated in the posterior portion. 5. The enzyme activity varies according to larval growth, being lower at the beginning of the fifth instar, higher after the middle of the instar, and again lower during cocoon-spinning. 6. The enzyme activity was concentrated 10 times by means of ammonium sulfate precipitation at a saturation of 0.375-0.425. Separation by the paper electrophoretic method was successfully applied for this fraction, but it was unsuccessful for separating β-glucosidase from other enzymes. 7. Virus-infected larvae showed a decrease in enzyme activity, compared with normal larvae. 8. β-Glucosidase activity in the digestive fluid was much lower than that in the midgut. A mutant, amylase-free strain possessed in the digestive fluid the same level of β-glucosidase activity as the normal one.

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