Studies of the intercellular matrix of growth plates from dwarf and homozygous nonaffected Alaskan Malamutes: collagen and hexosamine.

This study was performed to compare the extractability of dwarf growth plate collagen and hexosamine and that of homozygous nonaffected Malamutes and to measure the activity of three of the enzymes involved in the post-translational modifications of the collagen molecule. No significant differences were found in the activity of prolyl hydroxylase or lysyl oxidase in the dwarf growth plates. Lysyl hydroxylase activity in the dwarf was decreased to 22% and 33% that of the activity present in the homozygous nonaffected growth plates. Amino acid analysis of the collagen isolated from dwarf growth plates failed to reveal any decrease in hydroxylysine content. Growth plates were extracted with either 1 M sodium chloride or 4 M guanidine hydrochloride. The extracts were applied to a DEAE-cellulose column. Amino acid analyses of the material which did not bind to DEAE revealed a slight decrease in the amount of guanidine-extractable hydroxyproline in the dwarf but a 60-fold increase in the amount of salt-extractable hydroxyproline in the dwarf growth plates. Material which eluted with 1 M sodium choloride was analyzed for hexosamine. There was a 10-fold increase in the amount of salt-extractable hexosamine present in the dwarf growth plates, whereas no significant differences were observed in the guanidine-extracted material. Hexosamine analysis of the growth plates revealed a significant increase in the total amount of hexosamine present in the dwarf growth plates. SDS-polyacrylamide gels of the material which did not bind to DEAE as well as the pepsin digested, 0.9M sodium chloride precipitated collagen demonstrated the presence of only type II collagen.