Studies on the synthesis and secretion of trypsin in the midgut of Stomoxys calcitrans

Abstract

Iso-electric focusing of affinity-purified trypsin produced at least 15 bands which also stained positively in protease zymograms. Fresh homogenate containing unactivated trypsin produced bands which were missing from activated samples. Affinity purified, fully active trypsin separated by SDS-PAGE gave major bands with molecular weights of 22,900 and 31,600 daltons (Da). These bands were absent from unactivated homogenates which instead produced major protein bands at 24,700 and 33,500 Da. Tritium labelling experiments suggest there is a baseline level of asynchronous secretion from unstimulated opaque zone cells. While trypsin is stored as an inactive pro-enzyme it is secreted in a fully activated form. Inhibitor studies suggest the burst in trypsin synthesis immediately following the blood meal is regulated at the translational, rather than the transcriptional, level. Inhibitor studies show secretory granules in opaque zone cells are acidified by a strongly ATP-dependent proton pump.