Suggested assignment of peptidase S (PEPS) to 4q11-4q12 by exclusion using gene dosage, accounting for variability in fibroblasts

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Abstract
A colorimetric assay using leucyl-β-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→4q13 by exclusion. Combining these data with those previously reported, the suggested assignment for the PEPS locus is the 4p11→4q12 segment of chromosome 4.