Hydroxyproline biosynthesis

BARNETT N.M. 1970, Dipyridyl-induced cell elongation and inhibition of cell wall hydroxyproline biosynthesis. Plant Physiology, 45,... 

The triplet Cly-X-Y is constantly repeated in the sequence of the triple-helical regions— i. e., every third amino acid in such sequences is aglycine. Proline (Pro) is frequently found in positions X or Y the Y position is often occupied by 4-hydroxyproline (4Hyp), although 3-hydroxyproline (3Hyp) and 5-hydroxylysine (5Hyl) also occur. These hydroxylated amino acids are characteristic components of collagen. They are only produced after protein biosynthesis by hydroxylation of the amino acids in the peptide chain (see p. 62). 

The present work was undertaken in an attempt to shed light on the mechanism of hydroxyproline formation in collagen biosynthesis and on the site of action of ascorbate. It was recognized that these phenomena were very likely to be closely interrelated. Proline labeled with tritium was used because it was anticipated that tritium released from proline during hydroxylation would appear in the tissue water as tritiated water. The use of tritiated proline in such a system might then provide a new parameter for following the hydroxylation reaction, provided that the formation of tritiated water was stoichiometrically related to the formation of hydroxyproline. Such an approach might conceivably permit the demonstration of hydroxylation and peptide bond formation as separate chemical steps. 

Figure 20.19 Biosynthesis and degradation of proline, hydroxyproline and ornithine. Proline oxidase and S-pyrroIine-5-carboxylic acid dehydrogenase are both mitochondrial enzymes. A and B indicate defects in hyperprolinemia I and II, respectively.

This enzyme is involved in collagen biosynthesis in mammals as well as the biosynthesis of hydroxyproline in plant cell wall proteins and bacterial actinomycins. 

It is the purpose of this review to outline critically the methods available for hydroxyproline assay, and to summarize the information obtained by hydroxyproline determinations in urine, plasma (or serum), and the tissues, with emphasis on understanding the physiological and pathological setting in which these measurements have been made. No attempt will be made to discuss recent developments in the chemistry (H3, H4) or the biosynthesis (Ul) of collagen, since thorough reviews of these topics are available. 

H13. Hurych, J., and Chvapil, M., The role of free hydroxyproline in the biosynthesis of collagen. Biochim. Biophys. Acta 107, 91-96 (1965). 

G7. Gould, B. S., Biosynthesis of collagen. III. The direct action of ascorbic acid on hydroxyproline and collagen formation in subcutaneous polyvinyl sponge implants in guinea pigs. J. Biol. Chetn. 832, 637-649 (1958). 

Difluoroproline (22) was first reported in 1977, synthesized as apotential inhibitor of collagen biosynthesis. The chiral tricyclic diketopiperazine was prepared from (25,4/ )-4-hydroxyproline methyl ester and oxidized to the chketone. Fluorination with sulfur tetrafluoride and hydrolysis produced 22 (Fig. 3.10). 

The basic structure of collagen consists of the protofibril—a triple helix consisting of two identical a chains, as they are called, and one different chain. The a i chain of calf or rat hide consists of 1 052 a-amino acid residues, of which 1 001 are triplets of the general structure (gly-X-Y). Here, X may be proline, leucine, phenyl alanine, glutamic acid, and Y is mostly hydroxy-proline or arginine. Collagen is the only protein to contain hydroxyproline. This imino acid residue, however, is only formed after the protein biosynthesis. The triplets are, in turn, joined in sequences of polar and apolar regions. Telopeptides, peptide structures without triplet structure, occur at the N- and C-terminal triplet structures. The telopeptides are rich in lysine and they account for the intra- and intermolecular covalent cross-links. 

Arrigoni, O., Arrigoni-Liso, R., and Calabrese, G., 1977, Ascorbic acid requirement for biosynthesis of hydroxyproline-containing proteins in plants, FEBS Lett. 82 135-138. 

Sadava, D., Walker, F., and Chrispeels, M. J., 1973, Hydroxyproline-rich cell wall protein (extensin) Biosynthesis and accumulation in growing pea epicotyls, Dev. Biol. 30 42-48. 

Gould, B. S., and Woessner, J. F., 1957, Biosynthesis of collagen. The influence of ascorbic acid on the proline, hydroxyproline, glycine and collagen content of regenerating guinea pig skin, J. Biol. Chem. 266 289-300. 

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