A. Lenaers

Collagen has been extracted from the skin of dermatosparaxic calves and fractionated by acrylamide-gel electrophoresis and CM-cellulose chromatography. This collagen contains in large proportion two additional types of α-chains, P-α1 and P-α2. The first, P-α1, ressembles α1, of a collagen extracted from the skin of a normal calf in its amino-acid composition but its molecular weight is 10% larger. The second, P-α2, is similar to a normal α2 in its amino-acid composition but its molecular weight is increased by 5%. The abnormal α-chains contain six to eight half cystine residues in p-α1 and one in p-α2. As seen under the electron microscope on segment long spacing, the dermatosparaxic collagen is 25 nm larger than the normal collagen and the in creased length results from extension of the polypeptide chain at the N-terminal extremity of the molecules. Although the collagen is less extractable from the dermatosparaxic skin than from the normal skin and dimers and other polymers of the abnormal α-chains are observed, the dermatosparaxic collagen does not, in vitro, form fibrils of normal stability. Since an enzyme activity which can excise the N-terminal extension peptide of the dermatosparaxic collagen has been identified in extracts of normal skin but is absent in the dermatosparaxic animals, it is suggested that the dermatosparaxic collagen is a form of “procollagen”, from which all or a part of these peptides have not been removed and that such peptides function as coordinators in the post synthesis assembly of the collagen α-chains.

A heritable connective tissue disorder of cattle, dermatosparaxis, is characterized by an extreme fragility of the skin and the presence of additional peptides at the N-terminal extremities of the collagen alpha chains, p-alpha(1) and p-alpha(2). The existence of an enzyme activity is demonstrated in normal connective tissues that is capable of cleaving these additional N-terminal peptides from dermatosparaxic collagen. The activity is demonstratable with dermatosparaxic collagen in solution, as well as with reconstituted dermatosparaxic collagen fibrils polymerized in vitro. It has a pH optimum of about 7.0 and is inhibited by EDTA and mercaptoethanol. Differences in K(m) and V(max) values exist depending on the substrate utilized, i.e., p-alpha(1) or p-alpha(2); and the presence of additional amounts of one substrate, p-alpha(1), alters the concentration requirement for the second substrate, p-alpha(2). The product of the excision reaction with p-alpha(1) as substrate is an equimolar amount of normal alpha(1) monomer; the product when p-alpha(2) is substrate is an equimolar amount of normal alpha(2) monomer. The enzyme is present in normal calf skin, tendon, aorta, cartilage, and lung; it can be demonstrated in the skin of rats and humans. The enzyme activity is absent in dermatosparaxic connective tissues, thus suggesting that dermatosparaxis is caused by the absence of a normal enzyme function rather than by the production of an abnormal collagen.

The procollagen peptidase activity of calf tendon has been purified. The enzyme has a high degree of specificity for native procollagen and converts both pro alpha1 and alpha2, to alpha1 and alpha2, respectively. The purified enzyme is an endopeptidase which excises the amino terminal peptide extensions of the precursor chains in block; the molecular size and amino-acid composition of the excised peptides compare favorably with those predicted in previous reports. Antisera to the enzyme and to procollagen have been prepared and have been used to characterize the enzyme, the enzymatically excised peptides, and the enzyme-peptide complex in reaction mixtures.