AGMATINASE ACTIVITY IN RAT-BRAIN - A METABOLIC PATHWAY FOR THE DEGRADATION OF AGMATINE

Agmatinase, the enzyme that hydrolyzes agmatine to form putrescine and urea in lower organisms, was found in rat brain. Agmatinase activity was maximal at pH 8-8.5 and had an apparent K-m of 5.3 +/- 0.99 mM and a V-max of 530 +/- 116 nmol/mg of protein/h. After subcellular fracti onation, most of the enzyme activity was localized in the mitochondria l matrix (333 +/- 5 nmol/mg of protein/h), where it was enriched compa red with the whole-brain homogenate (7.6-11.8 nmol/mg of protein/h). W ithin the CNS, the highest activity was found in hypothalamus, a regio n rich in imidazoline receptors, and the lowest in striatum and cortex . It is interesting that other agmatine-related molecules such as argi nine decarboxylase, which synthesizes agmatine, and I-2 imidazoline re ceptors, for which agmatine is an endogenous ligand, are also located in mitochondria. The results show the existence of rat brain agmatinas e, mainly located in mitochondria, indicating possible degradation of agmatine by hydrolysis at its sites of action.