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

MAO activity against tryptamine was determined radiochemically in liver of lamprey (Lampetra zanandreai) larvae. The K-m and V-max values obtained were 289+/-31 mu M and 1.7+/-0.2 nmol /mg protein/min respectively. Activity was inhibited by different concentrations of clorgyline and (-)deprenyl with single sigmoid inhibition curves and the sensitivity to the two inhibitors was almost identical. The inhibition of tryptamine deamination by clorgyline and (-)deprenyl was non competitive after preincubation with the inhibitors, but was competitive without preincubation. Treatment with the non-ionic detergent Triton X-100 as well as causing a dose-dependent inhibition of MAO activity also causes a slight decrease in the sensitivity to clorgyline and (-)deprenyl. These results suggest that, at least under the experimental conditions adopted, liver MAO activity against tryptamine in larvae of Lampetra zanandeai is due to a single enzyme form related to but distinct from MAO A and MAO B.