Prolinarylamidase in Humanserum

Abstract

The catalytic concentrations of proline arylamidase in human sera were determined with L-proline-beta-naphthylamide (endpoint-method) and L-proline-p-nitranilide (continuous reaction). The continuous method was optimized: Tris-HCl, 40 mmol/l, pH 7,2; [S] = 1.53 mmol/l; T = 37 degrees C, t = 5-15 min, no additives. The pH-optimum was found to be 7.20; substrate excess inhibition was not observed. Tris-(hydroxymethyl)-aminomethane und N-morpholino-3-propane sulfonic acid buffers gave similar reaction rates. Reducing substances, SH-reagents, complex-forming or buffer substances, anticoagulants, proteinase inhibitors and the chlorides of Na+, Cu++, Mn++ and Ni++ did not influence the activity of the enzyme. Slight activation by the chlorides of Cd++, Zn++, Hg++, Co++, Mg++ and Ca++ could not be clearly differentiated from the effects of metalloproteinate formation. EDTA and benzethonium chloride inhibited the catalytic activity. In human sera no low molecular weight inhibitors were detectable. Catalytic concentrations were usually in the range below 10 U/l (37 degrees C). The coefficients of variation were found to be 9.1% intraserial and about 14.5% day-to-day. The preliminary upper limit of "normal" range was established as 8.0 U/l (37 degrees C). Comparative simultaneous determinations of the catalytic concentrations, using L-leucine-, L-alanine-, glycine, gamma-L-glutamic- and L-proline-p-nitranilide in the sera of 372 patients, suggest a special diagnostic role for proline arylamidase. The continuous method has been adapted for Vitatron-AKES-Analyser.