Dermatosparaxis in a Himalayan cat: I. Biochemical studies of dermal collagen.

Dermatosparaxis, a genetic disease, results from the deficiency of the NH2 procollagen peptidase, an enzyme which removes the NH2-terminal nontriple-helical extensions from procollagen. We have identified a Himalayan cat which has deficient amino terminal procollagen peptidase activity. The partially processed precursor chains pNalpha 1 (110,000 daltons) and pNalpha 2 (99,000 daltons) were identified by sodium dodecyl sulfate electrophoresis. In contrast to that from a normal animal, the 20,000 xg supernatant of a skin homogenate failed to convert pNcollagen to collagen. Amino acid analysis of pNalpha 1 and pNalapha 2 chains demonstrated the presence of cysteine and a lower percentage of hydroxyprolyl and glycyl residues due to the presence of the amino terminal extensions. The disorder in this animal is milder than that in sheep and cattle which is reflected in the longer survival and relatively smaller proportion of pNalpha chains in skin. The defect was also demonstrated by skin fibroblasts in culture.