Characterization of peptide alpha-amidation activity in human cerebrospinal fluid and central nervous system tissue

Peptidy-glycine α-amidation activity has been detected in human cerebrospinal fluid (CSF) and in several regions of the central nervous system. Activity was monitored by measuring conversion of mono-¹²⁵I-D-Tyr-Val-Gly into mono-¹²⁵I-D-Tyr-Val-NH₂. The α-amidation activity in CSF is dependent on molecular oxygen, copper ions and ascorbic acid and appears to recognize a variety of peptide substrates which contain carboxyl terminal glycine residues. Kinetic analyses demonstrated Michaelis-Menten kinetics with a K(m) of 4.6 μM for D-Tyr-Val-Gly. The level of peptidyl-glycine α-amidation activity in 14 samples of CSF averaged 43 ± 5 pmol/ml/h (mean ± SEM; range 11-85 pmol/ml/h) or 1.9 ± 0.2 pmol/mg protein/h. No difference was noted between samples from male and female subjects. Extracts of central nervous system tissue contained α-amidation activity. The highest levels of enzyme activity were found in the hypothalamus with lower levels in the neurohypophysis and the cerebral cortex. Still lower but detectable activity was found in the cerebellum and pons. Human peptidyl-glycine α-amidation activity is found in central nervous system tissues known to synthesize α-amidated neuropeptides and may be secreted from these tissues along with α-amidated peptides into CSF.