Ichishima E, Emi M, Majima E, Mayumi Y, Kumagai H, Hayashi K, Tomoda K. Initial sites of insulin cleavage and stereospecificity of carboxyl proteinases from Aspergillus sojae and Pycnoporus coccineus.
BIOCHIMICA ET BIOPHYSICA ACTA 1982;
700:247-53. [PMID:
7034782 DOI:
10.1016/0167-4838(82)90104-2]
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Abstract
Initial cleavage sites of native insulin at a pH of about 3 and stereospecificity were investigated by fungal carboxyl proteinases (EC 3.4.23.6) from ASpergillus sojae, a species of fungi imperfecti, and Pycnoporus coccineus (formerly designated Trametes sanguinea), a wood deteriorating Basidiomycete, respectively. Fungal carboxyl proteinases were used as a model of vertebrate insulin degradation. A. sojae carboxyl proteinase I primarily hydrolyzed two peptide bonds located on the surface of native insulin monomer, the B16-B17 (Tyr-Leu) and B24-B25 (Phe-Phe) bonds, and secondarily the buried bonds, A15-A16 (Gln-Leu), B15-B16 (Leu-Tyr) and B14-B15 (ala-Leu), at pH 3.2 and 30 degree C. The initial cleavage sites of A. sojae carboxyl proteinases I towards native insulin were not identical with the initial cleavage sites towards the oxidized B chain of insulin. P. coccineus carboxyl proteinase Ia selectively hydrolyzed B14-B15 (Ala-Leu), B16-B17 (Tyr-Leu) and B24-B25 (Phe-Phe) bonds in the native insulin at pH 2.7. Based on these findings we suggest that the stereospecificity of the fungal carboxyl proteinases is similar to that of cathepsin D (EC 3.4.23.5), and that the synthesis and degradation of insulin may occur in microorganisms.
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