THE NOVEL TYPE-II PROLYL 4-HYDROXYLASE IS THE MAIN ENZYME FORM IN CHONDROCYTES AND CAPILLARY ENDOTHELIAL-CELLS, WHEREAS THE TYPE-I ENZYME PREDOMINATES IN MOST CELLS

Procollagen-proline dioxygenase (EC 1.14.11.2), an alpha(2) beta(2) te tramer in vertebrates, plays a central role in the synthesis of all co llagens. Recently an isoform of the alpha subunit, the alpha(II) subun it, was characterized in man and mouse and found to form a tetramer wi th the same beta subunit as the previously known alpha(I) subunit, We report here that the (alpha(I))(2) beta(2) type I tetramer is the main enzyme form in most cell types and tissues and that its contribution to total prolyl 4-hydroxylase activity in cultured cells increases in confluence. Surprisingly, however, the (alpha(II))(2) beta(2) type II enzyme was found to represent at least about 70% of the total prolyl 4 -hydroxylase activity in cultured mouse chondrocytes and about 80% in mouse cartilage, the corresponding percentage in mouse bone being abou t 45% and that in many other mouse tissues about 10% or less. Immunofl uorescence studies on samples from a fetal human foot confirmed these data and additionally indicated that the type II enzyme represents the main or only enzyme form in capillary endothelial cells. Thus the typ e II, prolyl 4-hydroxylase is likely to play a major role in the devel opment of cartilages and cartilaginous bones and also of capillaries.