Inhibition of brain tubulinyl‐tyrosine carboxypeptidase by endogenous proteins

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Abstract
When a 25–50% ammonium‐sulphate‐insoluble fraction from a bovine brain preparation was chromatographed on a cellulose phosphate column, several protein fractions which inhibit the activity of tubulinyl‐tyrosine carboxypeptidase were obtained. One of these fractions exhibited activity of fructose‐bisphosphate aldolase (EC 4. 1. 2. 13) and the enzyme accounted for more than 95% of the protein of this fraction as judged by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis. The inhibitory activities of the two protein fractions which had the highest activity per mg of protein were practically abolished by pretreatment with pronase; preincubation with trypsin, on the other hand, caused only a partial inactivation of the inhibitors. The inhibitory activities were little affected by heating at 90°C for 5 min. Preincubation with purified tubulinyl‐tyrosine carboxypeptidase caused a great decrease of the inhibitory activities of these two fractions, leaving open the possibility that these inhibitors act as substrates of the carboxypeptidase.