K. Kivirikko, T. Helaakoski, K. Tasanen
Feb 1, 1990
Citations
3
Influential Citations
71
Citations
Quality indicators
Journal
Annals of the New York Academy of Sciences
Abstract
Prolyl 4-hydroxylase (EC I. 14.1 1.2) catalyzes the formation of 4-hydroxyproline in collagens and other proteins with collagen-like amino acid sequences by the hydroxylation of proline residues in -X-Pro-Glysequences. The enzyme plays a central role in collagen synthesis, as the hydroxyl groups of the 4-hydroxyproline residues are essential for the folding of the newly synthesized procollagen polypeptide chains into triple-helical molecules at body temperature. This crucial function of 4-hydroxyproline in collagens makes prolyl 4-hydroxylase a potential target for pharmacological modulation of the excessive collagen formation found in patients with various fibrotic diseases and has prompted numerous studies on the enzyme (for reviews on prolyl 4-hydroxylase, see Refs. 1-4). Prolyl 4-hydroxylase requires Fe2+, 2-oxoglutarate, 0,, and ascorbate. The 2oxoglutarate is stoichiometrically decarboxylated during hydroxylation, with one atom of the 0, molecule being incorporated into the succinate while the other is incorporated into the hydroxyl group formed on the proline residue.14 Ascorbate is a highly specific requirement, but it is not consumed stoichiometrically, and the enzyme can catalyze its reaction for a number of catalytic cycles in the absence of ascorbate. The reaction requiring ascorbate is probably an uncoupled decarboxylation of 2-oxoglutarate-that is, decarboxylation without subsequent hydroxylation of a proline re~idue?~ Prolyl4hydroxylase catalyzes such uncoupled decarboxylation cycles even in the presence of a saturating concentration of its peptide substrate, and hence the main biological function of ascorbate in the prolyl 4-hydroxylase reaction seems to be to act as an alternative oxygen acceptor in the uncoupled catalytic The active prolyl4-hydroxylase in vertebrates is a tetramer (I@,) with a molecular weight of about 240,000 and consisting of two different types of inactive monomer with molecular weights of about 64,000 (a subunit) and 60,000 (p subunit). The enzyme tetramer has two catalytic sites-one catalytic site per pair of dissimilar subunit^.^.^ Binding studies with different suicide inactivators of prolyl 4-hydroxylase7-’ and photoaffinity labeling studies’”’ with analogs of 2-oxoglutarate and the peptide substrate indicate that the 2-0xoglutarate’.~ and peptide’.’’ binding sites of the enzyme are located on the a subunit, whereas the ascorbate binding sites” may be built up of