Molecular physiology on H^+-translocating vacuolar-type ATPase in silkworms

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The silk gland in silkworms (the silk proteins, fibroin and sericin, factory) is an unique and indispensable tissue to produce the cocoons. The gland secretes and temporally stores the silk proteins within the glandular lumen without any denaturation of proteins till the silkworm starts to spin. The concentrations in the secreted protein reach up to 20-30% levels. Such a high concentration of the protein solution has to be regulated with a certain pH levels and a fixed water contents. We have investigated such a mechanism to understand the- ionic homeostasis and osmoregulation in the silk gland. Results are as-follows :(1) Immunocytochemicat studies were done with the specific antibody against Y-ATPase.. The V-ATFase can be- detected in the silk gland. V-A-TPase was located at the cell surface, suggesting that silkworm V-ATPases is a plasm a membrane-type not an endomanbrane-type.(2) In the silk gland, V-ATPase seems to contribute to produce an acidic milieu in the glandular lumen. This shows highly contrast to the lepidopteran midgut lumen, which produces. an extremely high alkalinity (pH-11-12).(3) The silk gland V-ATPase is quite-similar to other animal V-ATPase sharing the common subuits of V-ATPase.(4) The silk gland is a highly active tissue for silk protein syntesis and secretion The V-ATPase has to energize the plasma membrane and this supports that the active-amino acid transport from the haemolymph in order to synthesize the silkproteiri. Thus it is coming up as the near future subject to survey the K+/amino acid symporter in the silkgland. This would be expected as The breakthrough for identifying the K+/symportev molecule(s).