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Pacifastin is a family of serine proteinase inhibitors found in arthropods.〔 〕〔 〕 Pacifastin inhibits the serine peptidases trypsin and chymotrypsin.〔 〕 All pacifastin members that have been characterized at the molecular level are precursor peptides composed of an N-terminal signal sequence followed by a precursor domain and a variable number of inhibitor domains. Each of these inhibitor domains carries a six-cysteine motif - see below. The first family members to be identified were isolated from ''Locusta migratoria migratoria''(migratory locust) which were HI, LMCI-1 (PMP-D2) and LMCI-2 (PMP-C).A further five members, SGPI-1 to 5, were then isolated from ''Schistocerca gregaria'' (desert locust), and a heterodimeric serine protease inhibitor was isolated from the haemolymph of ''Pacifastacus leniusculus'' (Signal crayfish), and named pacifastin. ==Function== Peptide proteinase inhibitors are in many cases synthesised as part of a larger precursor protein, referred to as a propeptide or zymogen, which remains inactive until the precursor domain is cleaved off in the lysosome, the precursor domain preventing access of the substrate to the active site until necessary. Proteinase inhibitors destined for secretion have an additional N-terminal signal-peptide domain which will be cleaved by a signal-peptidase. Removal of these one or two N-terminal inhibitor domains, either by interaction with a second peptidase or by autocatalytic cleavage, will activate the zymogen.〔 〕 Very little is known about the endogenous function of pacifastin-like inhibitors except that they may play roles in arthropod immunity and in regulation of the physiological processes involved in insect reproduction.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pacifastin」の詳細全文を読む スポンサード リンク
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