Plasma pyridoxal 5'-phosphate concentrations in relation to apo-aminotransferase levels in normal, uraemic, and post-myocardial infarct sera.

The concentrations of pyridoxal 5'-phosphate, and the holoenzyme activities and apoenzyme contents of alanine aminotransferase and aspartate aminotransferase in plasma were determined simultaneously in healthy individuals, patients with renal insufficiency with and without chronic haemodialysis and in patients with acute myocardial infarction. Plasma pyridoxal 5'-phosphate is significantly diminished in uraemic patients and in post-myocardial infarct sera, healthy females have lower pyridoxal 5'-phosphate levels (26.2 +/- 9.0 nmol/l) than healthy males (41.0 +/- 15.1 nmol/l). The stimulation in vitro of the activities of aspartate aminotransferase and alanine aminotransferase by addition of pyridoxal 5'-phosphate (0.1 mmol/l) was found to be independent of the endogenous coenzyme level. In sera of uraemic patients without chronic haemodialysis an inverse statistic correlation between pyridoxal 5'-phosphate-induced stimulation of aspartate aminotransferase activity and the concentrations of urea (r = -0.696) and creatinine (r = -0.715) was found. The respective correlations are much weaker for alanine aminotransferase. The apoenzyme fraction was highest in post-myocardial infarct sera. Follow up of these patients did not reveal any relationship between the fluctuations of pyridoxal 5'-phosphate levels and apoenzyme contents of both alanine aminotransferase and aspartate aminotransferase. The results permit the conclusion that the degree of in vitro stimulation of aminotransferases by pyridoxal 5'-phosphate can not be predicted from the endogenous coenzyme level.