Enzymatic and Metabolic Studies of Homocystinuria: Effects of Pyridoxine[*]

There is a wide spectrum of biochemical response to massive doses of pyridoxine in patients with homocystinuria. Metabolic and enzymatic studies in these patients, before and after such treatment, establish that the effect of pyridoxine, in the patient who responds, is not on cystathionine synthase of liver. In patients with homocystinuria treated with methionine-restricted diet, supplemented with cysteine, there is a striking reduction in activity of methionine-activating enzyme, as well as an absence of activity of cystathionine synthase. In patients with homocystinuria treated with pyridoxine over a long period of time, there is a dramatic increase in activity of cystathionase of liver. The formation of chemical artifacts in crude enzymatic extracts to which large amounts of pyridoxal phosphate are added, render interpretation of changes in activity of the affected enzyme in “pyridoxine-dependency” states equivocal, unless the product of the reaction is rigorously identified.

Homocystinuria - Cystathionine Synthase - Methionine-activating Enzyme - Cystathionase Pyridoxine-dependency - Pyridoxal Phosphate

1 Presented in part at the European Club for Pediatric Reserach, Vienna, August, 1968 and abstracted in Pediat.

1 Presented in part at the European Club for Pediatric Reserach, Vienna, August, 1968 and abstracted in Pediat.