Effects of oestrogen administration on vitamin B6 and tryptophan metabolism in the rat

1.In order to assess the effects of oestrogens on the metabolism of tryptophan and vitamin B6, ovariectomized rats have been maintained on diets providing known amounts of tryptophan, nicotinamide and vitamin B6. They received oestrone sulphate. 210μg/kg body-wt per d, either incorporated in the diet for 8 weeks, or by daily intraperitoneal injection for periods of 1–3 d.2. Oestrone sulphate administration caused a slight reduction in the concentration of pyridoxal phosphate in plasma. It had no effect on the concentration of pyridoxal phosphate in liver or kidney, the urinary excretion of 4-pyridoxic acid, the activation of erythrocyte aspartate aminotransferase (L-aspartate:2-oxo-glutarate aminotransferase, EC 2.6.1.1)by incubation with added pyridoxal phosphate, or the activity of pyridoxal oxidase (aldehyde:oxygen oxido-reductase, EC 1.2.3.1) in the liver.3. Oestrone sulphate administration caused an increase in the urinary excretion of kynurenine and a reduction in the activity of liver kynureninase (L-kynurenine hydrolase, EC 3.7.1.3), It had no effect on the urinary excretion of N1-methyl nicotinamide or the concentrations of nicotinamide nucleotides in blood, liver or kidney.4. There was a considerable excess of the apoenzyme of kynureninase in the liver. Incubation of liver homogenates with added pyridoxal phosphate led to a 4- to 5-fold increasein activity.5. We conclude that there is no evidence of any significant effect of oestrogens on vitamin B6. It is suggested that abnormalities of tryptophan metabolism in women receiving oestrogens. which have been widely attributedto drug-induced vitamin B6 depletion, can be accounted for by inhibition of kynureninase by oestrogen metabolites.

GENETIC CONTROL OF ALDEHYDE OXIDASE ACTIVITY AND CROSS-REACTING-MATERIAL IN DROSOPHILA MELANOGASTER

Four different genes are known to affect aldehyde oxidase activity (AO) in Drosophila melanogaster. Mutants at each of these loci eliminate AO activity and simultaneously eliminate detectable AO-crossing reacting material (AO-CRM) even though only one is the structural gene for AO (Aldoxn). The other three genes (cin1, lxd and mal) coordinately "control" the levels of activity of AO and two related enzymes, xanthine dehydrogenase (XDH) and pyridoxal oxidase (PO). Contrary to their effects on AO-CRM, neither of these three mutants eliminate XDH-CRM. A model of interaction of these enzymes and genes controlling their activities is discussed.