Summary:Arginine carboxypeptidase activity in human serum, measured with the hippuryl-L-arginine substrate, is about three times higher than in human plasma. This difference is much smaller when hippuryl-Llysine is used äs the Substrate. When fresh serum is incubated at 30 °C, the arginine and lysine carboxypeptidase activity decreases until a stable activity, close to the plasma activity, is reached. This stable carboxypeptidase activity is attributed to carboxypeptidase N. The unstable carboxypeptidase differs from carboxypeptidase N in pH-optimum, esterase activity, Substrate specifity, Co 2+ -activation and dithiotreitol activation. Blood cells are not responsible for the release of this enzyme during coagulation. No activator of carboxypeptidase N was detectable in human serum.-exchange chromatography on DEAE-cellulose confirms the presence of two different molecular forms of arginine carboxypeptidase activity.

No abstract

The proline-specific peptidases, aminopeptidase P (EC 3.4.11.9) and dipeptidyl peptidase IV (EC 3.4.14.5), were measured in human tissue homogenates and physiological fluids. All tissues examined contained measurable aminopeptidase P and dipeptidyl peptidase IV activities. High specific activities for both enzymes under study were found in benign prostatic hypertrophy. Normal prostate and prostatic adenocarcinoma had a much lower activity. This difference, however, is not reflected in the serum values of the patients. The most striking finding is the extremely high activity of dipeptidyl peptidase IV in prostatosomes, prostate-derived organelles, which occur freely in human seminal plasma, and which are important for enhancement of sperm forward motility.

No abstract

A new fluorometric assay for determining dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) was developed. The synthetic substrate glycyl-L-proline-4-methoxy-2-naphthylamide (20 mmol/L), Tris buffer (50 mmol/L, pH 8.3), and serum (20 microL) are mixed and incubated. The reaction is stopped with citrate (100 mmol/L, pH 4.0) and the released 4-methoxy-2-naphthylamine is measured fluorometrically. The mean value of DPP IV activity in serum for 64 healthy subjects was 58 (SD 16) mumol of 4-methoxy-2-naphthylamine released per liter of serum per minute. The proposed procedure is sensitive, rapid, and accurate and can easily be automated.