Assay and biochemical characterization of angiotensin-I-converting enzyme in cerebrospinal fluid.

A spectrofluorimetric method was adapted for determination of angiotensin-I-converting enzyme (ACE) in untreated native cerebrospinal fluid (CSF). Benzyloxycarbonyl-phenylalanyl-histidyl-leucine was applied as enzyme substrate. The biochemical behavior of ACE of CSF (CACE) was studied. The pH optimum was found to be 8.0 using borax phosphate buffer. The determination of Km was 10.7 +/- 3.3 (SD) mumol/l. ACE could be blocked by 8-hydroxyquinoline (100%) and phenanthroline (80%), but only slight inhibition was observed by teprotide (43%), EDTA (40%) and captopril (31%). The influence of various drugs on CACE was also tested. The different biochemical behavior of CACE compared to serum ACE suggested that an isoenzyme exists in CSF. CACE has been found to be elevated in neuroimmunological and inflammatory disorders of the nervous system compared to levels in healthy controls.