Purification and characterization of a human NO synthase.

A NO synthase (NOS, EC 1.14.23) was isolated from human cerebellum by two sequential chromatography steps, that is affinity chromatography on 2'5'ADP sepharose and size exclusion chromatography on Superose 6. Human NOS migrated as a single band of 160 kDa on SDS/PAGE. The enzyme was Ca2+/calmodulin-regulated and NADPH/tetrahydrobiopterin (BH4)-dependent, which are characteristics of a type I NOS previously isolated from rat cerebellum. Antisera raised against purified rat cerebellar NOS crossreacted specifically with a 160 kDa protein in crude supernatant fraction of human cerebellum and purified human NOS but not in crude supernatant fraction of the temporal lobe. These findings provide evidence that nitrinergic signal transduction through conversion of L-arginine to L-citrulline and NO does also occur in humans and NO may function as a neurotransmitter in the human central nervous system.