Abstract
Cerebrospinal fluid (CSF) from dogs competitively inhibited A-form MAO, but was non-competitive with B-form MAO. Heat treatment of CSF (90°C, 20 min) had no effect on the inhibition. Digestion with trypsin and chymotrypsin reduced the MAO inhibitory activity. After ultrafiltration of the CSF through a membrane to remove substances of >5, 000 M.W., significant inhibitory activity persisted. These results suggest that CSF contains endogenous substances that act like MAO inhibitor to inhibit A and B-form MAO, and these substances are peptides of less than 5, 000 M.W.
