Goebelsrnann and Beller: Cystine-Amino-Peptidase and Leucine-Amino-Peptidase in pregnant and nonpregnant women

Serum leucine-aminopeptidase (LAP) and cystine-aminopeptidase (CAP) determinations have been made using a chemical method based on enzymatic hydrolysis of l-leucine-/?-naphthylamide-hydrochloride and cystine-di-/?naphthylamide, respectively. Fractionation of serum proteins by gel filtration on "Sephadex-G 200" has been used for separation of LAP and CAP (oxytocinase). — CAP which appears during pregnancy only and LAP present in all sera, hydrolyse both substrates, LNA and CDNA. LAP has been found to cleave LNA 74 times faster than CDNA and CAP has been confirmed to hydrolyse LNA 11 times faster than CDNA. CAP-activity found in non-pregnant serum with small, but significant values, is due to LAP hydrolysing CDNA. Comparing these CAP-activity values in normal individuals with CAP-activity levels at term, only a 13-fold increase of CAP-activity can be recovered. Subtraction of CAP-activity due to LAP from total CAP-activity in early pregnancy reveals against net CAP values at term an increase .of CAP activity which is comparable to ratios found with oxytocinase determinations based on a bioassay methods. — Separation of CAP from LAP on "Sephadex" gel dilutes small enzyme concentrations as appear during the first half of gestation to such an extent as to make pooling and concentration procedures necessary in order to achieve appreciable accuracy for CAP assays. The slow increase of CAP during the first half of gestation, the variation of LAP-activity in normal individuals and the mutual substrate unspecificity of both enzyme render LAP and CAP assays invalid for the diagnosis of early pregnancy.