Dermatosparaxis is a connective tissue disease, primarily of sheep and cattle, that results from deficient activity of the NH2-terminal procollagen peptidase. It is characterized by fragile, loose skin that is easily torn with minor trauma. We have identified a cat twith a defect in this procollagen peptidase which affects only a small proportion of the collagen molecules; the majority of the collagen is processed normally. Nonetheless, as seen by transmission and scanning electron microscopy, this population of aberrant collagen molecules significantly alters the structure of individual collagen fibrils, the assembly of fibrils into fiber bundles and the integration of fiber bundles into a normal, woven network in the reticular dermis of skin. Although the clinical findings are less severe than those in sheep and cattle where the enzymatic defect is more complete, the ultrastructural abnormalities are marked and demonstrate that a minority of abnormal collagen molecules cn have a major effect on the structure and function of connective tissues.

Prolyl hydroxylase (proline,2-oxoglutarate dioxygenase, EC 1.14.11.2) is a mixed-function oxygenase that hydroxylates peptidyl proline with the simultaneous and stoichiometric decarboxylation of a-ketoglutarate to succinate and CO2. It has been found that highly purified preparations of the enzyme can decarboxylate a-ketoglutarate in the absence of a peptidyl proline substrate. The uncoupled decarboxylation proceeds at only a fraction of the rate of the whole reaction and or study requires substrate quantities of the pure enzyme, as well as oxygen, ferrous ion, and ascorbate. No hydroxyproline is formed under these conditions. Immobilized antiserum to prolyl hydroxylase was found to remove both activities from enzyme preparations. However, addition of free antiserum during incubation inhibits only the complete reaction. Poly(Lproline), a specific inhibitor of prolyl hydroxylation, enhances the uncoupled decarboxylation of a-ketoglutarate without itself being hydroxylated. All of these findings prove that a-ketoglutarate can serve as substrate in the absence of peptidyl proline and is most likely the initial site of attack by oxygen. In the coupled reaction an oxidized form of the keto acid, perhaps a peroxy acid, then attacks prolyl residues in the unhydroxylated substrate. Prolyl hydroxylase (proline,2-oxoglutarate dioxygenase, EC 1.14.11.2) catalyzes the hydroxylation of peptidyl proline with the concomitant decarboxylation of a-ketoglutarate. For each mole of proline hydroxylated, one mole of a-ketoglutarate is stoichiometrically decarboxylated to succinate and carbon dioxide. The enzyme also has an absolute requirement for ferrous ion and a reducing agent (1).The hydroxyl group of the hydroxyproline is derived from molecular. oxygen (2, 3). After the specific and absolute requirement of the enzyme for a-ketoglutarate was discovered (1, 4), several other oxygenase systems that require a-ketoglutarate were described (5-9). Lindblad et al. (10) reported that 180 from molecular oxygen is incorporated not only into carnitine during the y-butyrobetaine hydroxylase reaction, but also into the succinate derived from a-ketoglutarate. Cardinale et al. (11) were able to demonstrate that prolyl hydroxylase catalyzes the incorporation of equal amounts of 180 into peptidyl hydroxyproline and into the succinate derived from aketoglutarate. On the basis of such findings, Holme et al. (12) proposed as a mechanism for the hydroxylation of y-butyrobetaine that a peroxide bridge is formed between the a-ketoglutarate and y-butyrobetaine. Such an intermediate could then dissociate to yield the hydroxylated 'y-butyrobetaine (carnitine) and succinate. It was proposed (12) that a hydroperoxide is first formed on y-butyrobetaine; this hydroperoxide could then attack a-ketoglutarate and the intermediate would then decompose to carnitine, succinate, and CO2. An analogous reaction mechanism, involving the initial formation of a hydroperoxide on the number four carbon of the prolyl residue, can be postulated for prolyl hydro...

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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.

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