Cerebral proteinases in the growing rat.

Abstract

Abstract—The proteolytic activity of brain homogenates obtained from 1‐, 5‐, 14‐, 60‐, 150‐, and 300‐day‐old rats was assayed with urea‐denatured haemoglobin and casein, endogenous tissue proteins, Nα‐benzoyl‐dl‐arginine 2‐naphtylamide (BANA), Nα‐benzoyl‐dl‐arginine methyl ester (BAME), Nα‐toluene p‐sulphonyl‐dl‐arginine methyl ester (TAME), Nα‐benzoyl‐dl‐phenylalanine 2‐naphthyl ester (BPANE), and Nα‐acetyl‐dl‐tyrosine ethyl ester (ATEE) as substrates.Several peaks of activity were detected with all these substrates in different pH ranges. Activity was highest with protein substrates at pH 3·0‐4·0, with smaller peaks of activity at pH 5·5‐6·5 and 8·0‐9·0. At pH 3·0 the activity with trypsin substrates, viz. BANA, BAME and TAME, was also relatively high, but much less with chymotrypsin substrates, ATEE or BPANE. With BAME, TAME, BPANE and ATEE the hydrolysis rate was highest at neutral or slightly alkaline pH. During postnatal development the hydrolysis of protein substrates increased three‐fold at pH 3·0 and about two‐fold at pH 6·5 and 8·5. The rate of hydrolysis of BANA, BAME and TAME generally increased during the first 2 postnatal weeks and thereafter decreased, whereas no marked increase in the rate of hydrolysis of BPANE and ATEE occurred until the age of about 2 weeks. The results were less consistent with synthetic substrates than with protein substrates, indicating the existence of non‐uniform alterations during development in the activity of the individual hydrolytic enzymes participating in the breakdown of brain proteins.