Friedman T C, Loh Y P, Birch N P
Section on Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Endocrinology. 1994 Sep;135(3):854-62. doi: 10.1210/endo.135.3.8070378.
The prohormone convertases, PC1 (SPC3) and PC2, are subtilisin-like serine proteases capable of processing neuropeptide precursors. In cotransfection experiments, other investigators have found that PC1 and PC2 can process POMC to appropriate peptide products. In this study, recombinant rat PC1 was stably expressed in a mouse L-cell line and partially purified. Mouse POMC was cleaved by recombinant PC1 to generate ACTH intermediates, ACTH, ACTH linked to joining peptide, joining peptide, 16-kilodalton N-POMC, N-POMC-(1-74), and beta-lipotropin. Recombinant PC1 was also found to cleave ACTH to ACTH-(1-15) and bovine N-POMC-(1-77) to gamma 3 MSH. The pH optimum of the cleavages was 6.0. We conclude that recombinant PC1 is capable of processing POMC in vitro at all of the paired basic residues, with the exception of Lys-Arg and Lys-Lys in beta-lipotropin and beta-endorphin, respectively. This in vitro study showed a more general specificity of recombinant PC1 for paired and tetrabasic residues of POMC than was previously found in cotransfection experiments. Other cellular regulatory mechanisms probably play a role in limiting the processing of POMC in vivo in the anterior pituitary, where gamma 3 MSH and alpha MSH are not found in significant amounts.
激素原转化酶PC1（SPC3）和PC2是类似于枯草杆菌蛋白酶的丝氨酸蛋白酶，能够加工神经肽前体。在共转染实验中，其他研究人员发现PC1和PC2可以将阿黑皮素原加工成合适的肽产物。在本研究中，重组大鼠PC1在小鼠L细胞系中稳定表达并部分纯化。重组PC1可切割小鼠阿黑皮素原，生成促肾上腺皮质激素中间产物、促肾上腺皮质激素、与连接肽相连的促肾上腺皮质激素、连接肽、16千道尔顿的N-阿黑皮素原、N-阿黑皮素原-（1-74）和β-促脂素。还发现重组PC1可将促肾上腺皮质激素切割成促肾上腺皮质激素-（1-15），并将牛N-阿黑皮素原-（1-77）切割成γ3促黑素细胞激素。切割的最适pH值为6.0。我们得出结论，重组PC1能够在体外切割阿黑皮素原所有成对的碱性残基，但β-促脂素中的赖氨酸-精氨酸和β-内啡肽中的赖氨酸-赖氨酸除外。这项体外研究表明，重组PC1对阿黑皮素原成对和四价碱性残基的特异性比以前在共转染实验中发现的更普遍。其他细胞调节机制可能在限制垂体前叶体内阿黑皮素原的加工中起作用，在垂体前叶中未发现大量的γ3促黑素细胞激素和α促黑素细胞激素。
