Rise in serum levels of PZ-peptidase, an enzyme involved in collagen breakdown, in human pregnancy and labor.

PZ-Peptidase is an enzyme capable of cleaving small peptides that are produced during the metabolic breakdown of collagen. It is conveniently assayed by use of the synthetic peptide 4-phenylazobenzyl-oxycarbonyl-L-prolyl-L-leucyl-glycyl-L-pro lyl-D-arginine. An improved assay is reported which permits measurements of small amounts of this enzyme in 0.1 ml of serum. The enzyme activity in serum was found to rise from 1.3 U/L (1 U = 1 mumol cleaved per minute) in nongravid patients to 4.0 U/L in patients at term, who display no objective or subjective signs of labor. Patients in active labor show a further elevation of activity to 6.5 U/L. These results are believed to reflect changes in collagen metabolism related to remodeling of the uterus and skeleton in pregnancy and to cervical dilatation and placental separation at the time of labor.