Abstract
We have reported previously that the inactive lectin isolated from the hemolymph of young fifth instar larvae of Bombyx mori was activated by a soluble fraction of the pupal fat body. Here, we tried to identify the factor activating the lectin. A pooled fraction considered to contain neuraminidase was obtained by gel filtration from the fat body on day 3 after pupation. Upon the hemagglutination assay against sheep blood cells, the pooled fraction activated the lectin as a standard neuraminidase would. Both the color reaction from thiobarbituric acid assay and HPLC analysis showed that the pooled fraction affected N-acetylneuraminyl α-(2→6)-lactose used as a substrate against neuraminidase. These results suggest the possibility that a neuraminidase-like enzyme exists in the fat body, and is indirectly related to humoral lectin activity in vivo. Conversely, α- and β-galactosidase activities were confirmed to be present in the hemolymph and fat body of larvae at the fifth instar. These activities were high on the spinning day (day 9 of the fifth instar). The β-galactosidase activity was higher than the α-galactosidase activity during the period examined. These observations are in agreement with the notion that galactosidases are involved in the inactivation of lectin activity.
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