THE OXIDATION OF TRYPTAMINE BY MONOAMINE-OXIDASE FROM LIVER OF LARVAEOF LAMPETRA-ZANANDREAI

MAO activity against tryptamine was determined radiochemically in live r of lamprey (Lampetra zanandreai) larvae. The K-m and V-max values ob tained were 289+/-31 mu M and 1.7+/-0.2 nmol /mg protein/min respectiv ely. Activity was inhibited by different concentrations of clorgyline and (-)deprenyl with single sigmoid inhibition curves and the sensitiv ity to the two inhibitors was almost identical. The inhibition of tryp tamine deamination by clorgyline and (-)deprenyl was non competitive a fter preincubation with the inhibitors, but was competitive without pr eincubation. Treatment with the non-ionic detergent Triton X-100 as we ll as causing a dose-dependent inhibition of MAO activity also causes a slight decrease in the sensitivity to clorgyline and (-)deprenyl. Th ese results suggest that, at least under the experimental conditions a dopted, liver MAO activity against tryptamine in larvae of Lampetra za nandeai is due to a single enzyme form related to but distinct from MA O A and MAO B.