Abstract
Although studies on the degradative metabolism of hydroxyproline have revealed that this amino acid is converted at least in part to glutamic acid (I-G), knowledge of the intermediates in this conversion and of other products of hydroxyproline metabolism is not yet complete. In the course of experiments on the metabolism of hydroxyproline, it was observed that incubation of hydroxyproline with kidney pre.parations led to the formation of a compound which we have identified as pyrrole-2-carboxylic acid (PCA) (7).’ Subsequent study revealed that kidney D-amino acid oxidase oxidizes hydroxy-n-proline and allohydroxy-n-proline to an intermediate compound which appears to be Al-pyrroline-4-hydroxy-2-carboxylic acid. The int’ermediate is spontaneously converted (at pH 8.3) to PCA; this conversion occurs much more rapidly in acid solution. PCA formation was also observed as a product of t,ransamination of y-hydroxyornithine with glyoxylate, pyruvate, or wketoglutarate. The evidence suggests that such transamination, in contrast to that of ornithine (8, 9), involves the a-amino group rather than the b-amino group. This report describes experiments on the formation of PCA by enzymatic oxidation, by enzymatic and non-enzymatic transamination, and also by non-enzymatic oxidation of hydroxyproline by hydrogen peroxide. Some implications of these findings in terms of the metabolism of hydroxyproline are discussed.
Highlights
In the course of experiments on the metabolism of hydroxyproline, it was observed that incubation of hydroxyproline with kidney pre.parations led to the formation of a compound which we have identified as pyrrole-2-carboxylic acid (PCA)
Calculation of PCA from the maximal absorption observed (Curve 5) showed the presence of 4.3 pmoles of PCA, in good agreement with the data for oxygen uptake (Fig. 2). These results suggest the formation of an intermediate compound which was converted to PCA
(presumably the dihydroquinazolinium derivative formed by condensation of o-aminobenzaldehyde and the Al-pyrroline compound [19, 20]) were chromatographed in several solvents together with the intensely colored yellow compound formed by the reaction of o-aminobenzaldehyde with the intermediate formed in the oxidation of hydroxyproline by D-amino acid oxidase
Summary
Studies on the degradative metabolism of hydroxyproline have revealed that this amino acid is converted at least in part to glutamic acid (I-G), knowledge of the intermediates in this conversion and of other products of hydroxyproline metabolism is not yet complete. In the course of experiments on the metabolism of hydroxyproline, it was observed that incubation of hydroxyproline with kidney pre.parations led to the formation of a compound which we have identified as pyrrole-2-carboxylic acid (PCA). This report describes experiments on the formation of PCA by enzymatic oxidation, by enzymatic and non-enzymatic transamination, and by non-enzymatic oxidation of hydroxyproline by hydrogen peroxide. Some implications of these findings in terms of the metabolism of hydroxyproline are discussed
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