KYOTORPHIN SYNTHETASE-ACTIVITY IN RAT ADRENAL-GLANDS AND SPINAL-CORD

Kyotorphin, an endogenous [Met(5)]enkephalin-releasing antinociceptive dipeptide (L-Tyr-L-Arg), is formed by kyotorphin synthetase from its constituent amino acids, L-Tyr and L-Arg, in the brain in an ATP-Mg2+- dependent manner. To elucidate the physiological role of kyotorphin in organs other than the brain, we examined the activity of kyotorphin s ynthetase in the rat adrenal glands and spinal cord. By Sephacryl S-30 0 gel-filtration chromatography of the soluble extracts from both the organs, the enzyme activity forming immunoreactive kyotorphin from L-T yr and L-Arg in the presence of ATP and MgCl2 was detected in the frac tions with the molecular mass of 200-300 kDa, being drastically reduce d by the omission of ATP and MgCl2 from the reaction medium. The K-m v alues of the partially purified adrenal and spinal kyotorphin syntheta se for L-Tyr, L-Arg, ATP, and MgCl2 were close to those of the brain e nzyme. The activity of adrenal kyotorphin synthetase was inhibited by some L-Arg analogues, N-G-nitro-L-arginine methyl ester, alpha-methyl- L-ornithine and D-Arg, but not by N-G-nitro-L-arginine and N-iminoethy l-L-ornithine. In the crude soluble extracts from the adrenal glands a nd spinal cord, kyotorphin was formed by kyotorphin synthetase, and al so by the enzymatic processing of the precursor proteins, in the prese nce of physiological concentrations of L-Tyr and L-Arg in addition to ATP and MgCl2. Thus, kyotorphin synthetase resembling that in the brai n is present in the rat adrenal glands and spinal cord. The present fi ndings may predict a functional role of the L-Arg-kyotorphin pathway i n these organs.