Suggested assignment of peptidase S (PEPS) to 4p11-4q12 by exclusion using gene dosage, accounting for variability in fibroblasts.

A colorimetric assay using leucyl-beta-napthylamide hydrochloride as substrate and fast garnet GBC as the color reagent was developed for these regional mapping studies of peptidase S (PEPS). PEPS activity was measured in white blood cells from three patients with Wolf-Hirschhorn syndrome (4p-) and 50 controls. The enzyme activity of the three patients, mean 0.097 +/- 0.060 (SD) did not exhibit a significant dosage effect compared to the controls, mean 0.125 +/- 0.060 (SD) mIU/mg protein. Peptidase activity was compared among five fibroblast control lines and eight lines with chromosome 4 aberrations. There was no significant difference found among the 128 samples from aberrant lines, mean of partial monosomies = 0.095 +/- 0.049 (SD) and mean of partial trisomies = 0.084 +/- 0.046 (SD) and the 79 samples from control lines, mean = 0.092 +/- 0.043 (SD) mIU/mg protein. Degree of confluence, site of biopsy, and sex and age of donor did not affect PEPS activity in fibroblasts but generation number did (r = 0.367, P = 0.001). No gene dosage was found in the white blood cells or fibroblast lines studied. The locus for PEPS is therefore mapped to 4p11 leads to 4q13 by exclusion. Combining these data with those previously reported, the suggested assignment for the PEPS locus is the 4p11 leads to 4q12 segment of chromosome 4.