Dependence of an alkyl glycol-ether monooxygenase activity upon tetrahydropterins.

Glyceryl-ether monooxygenase (1-alkyl-sn-glycerol,tetrahydropteridine: oxygen oxidoreductase, EC 1.14.16.5) catalyzes the oxidative cleavage of 1-O-alkyl glycerol or glycol derivatives to a long-chain aldehyde and the glycerol or glycol derivative. The specificity for tetrahydropterins of a similar, perhaps identical, enzyme that cleaves O-hexadecyl ethylene glycol in rat liver microsomes was examined with the use of an assay based on [1-3H]ethylene glycol formation from 2-hexadecyloxy [1-3H]ethan-1-ol. Several tetrahydropterin derivatives are effective electron donors for this reaction, and 2,4,5-triamino-6-hydroxypyrimidine is somewhat effective, but NADH, NADPH, ascorbate, reduced dichlorophenolindophenol and glutathione are inactive. Tetrahydropterin derivatives differ from each other in apparent Km and apparent Vmax. The order of increasing apparent Km values is tetrahydropterin approximately 6-methyltetrahydropterin approximately tetrahydrobiopterin less than 6.7-dimethyltetrahydropterin less than tetrahydrofolate. The order of increasing apparent Vmax values is tetrahydrofolate approximately tetrahydropterin less than 6-methyltetrahydropterin approximately tetrahydrobiopterin approximately 6,7-dimethyltetrahydropterin. Results obtained with the use of a spectrophotometric assay, in which tetrahydropterin oxidation is coupled to NADH oxidation by dihydropteridine reductase (NAD(P)H: 6,7-dihydropteridine oxidoreductase, EC 1.6.99.7), indicated that the ratio of 6,7-dimethyltetrahydropterin or 6-methyltetrahydropterin oxidized to ether lipid degraded is about 1.1 to 1.3. Unlike cytochrome P-450-dependent hydroxylases, this alkyl glycol-ether monooxygenase is not inhibited by carbon monoxide. 1-O-hexadecyl-rac-glycerol (chimyl alcohol) competitively inhibits the oxidation of the glycol ether indicating that the same enzyme probably catalyzes the oxidation of both O-alkyl glycol and 1-O-alkyl glycerol.

Hyperphenylalaninemia due to dihydropteridine reductase deficiency: diagnosis by measurement of oxidized and reduced pterins in urine.

Hyperphenylalaninemia due to dihydropteridine reductase deficiency results from the inability to maintain the aromatic amino acid hydroxylase cofactor, tetrahydrobiopterin, in its reduced or active form. Diagnosis of the disease is usually made by direct enzymatic assay on liver biopsies or in cultured skin fibroblasts. Evidence is presented that normal children and classic phenylketonuric children excrete mainly tetrahydrobiopterin in their urines, whereas children with dihydropteridine reductase deficiency excrete only oxidized forms of biopterin. Details of a rapid high performance liquid chromatographic assay for the measurement of the various forms of biopterin in urine are presented. This assay can be used to screen for suspected dihydropterine reductase mutants.

Hyperphenylalaninemia due to a deficiency of biopterin. A variant form of phenylketonuria.

We studied the components of the hepatic phenylalanine hydroxylating system in a child with phenylketonuria who showed substantial neurologic impairment despite early dietary control of elevated blood phenylalanine levels. Phenylalanine hydroxylase, dihydropteridine reductase and dihydrofolate reductase activities were normal. In contrast the level of hydroxylation cofactor, tetrahydrobiopterin, in liver was only 10 per cent of normal. In addition to this hepatic deficiency, serum and urinary levels of biopterin-like compounds were low, and the serum biopterin did not increase in response to a phenylalanine load as it does in normal and phenylketonuric subjects. The phenylalanine hydroxylase activity in this child, as determined by an in vivo tritium-release assay, was 2.3 per cent of the normal value. These results indicate that the child suffers from a variant form of phenylketonuria--a deficiency of a functional phenylalanine hydroxylating system secondary to a defect in biosynthesis of biopterin.

Hyperglycinuria and hyperglycinemia in two siblings with mild developmental delays.

Two preschool-age siblings with similar histories of encephalopathy were examined for developmental retardation and found to have elevated levels of urinary and blood glycine. Their inability to convert glycine into serine in the absence of elevated blood and urinary ketone levels was suggestive of a defect in the glycine-cleavage enzyme system (or serine hydroxymethyl transferase). These patients differ significantly from the majority of reported cases of nonketotic hyperglycinemia in that they did not manifest life-threatening neonatal illness, severe mental retardation, or neurological deficits. However, during an oral glycine load, alterations in the electroencephalographic pattern occurred that suggested a relationship between elevated blood glycine levels and pathological involvement of the central nervous system. The ratio of CSF-blood glycine was found to be in the range expected for nonketotic hyperglycinemia.

Automated fluorometric analysis of galactose in blood.

In galactosemia, prevention of mental retardation depends on early recognition of the disorder and institution of dietary restriction of galactose. We describe an automated fluorometric micromethod for galactose in whole blood spotted on filter paper. Galactose is oxidized by galactose oxidase to D-galacto-hexadialdose and H2O2 and measured as the highly fluorescent condensation product of homovanillic acid formed when H2O2 is acted upon by horseradish peroxidase. The procedure is 10-fold more sensitive than colorimetric procedures for galactose and is not hampered by the nonspecific fluorescence from endogenous NADPH that is encountered in methods in which galactose dehydrogenase is used. At a sampling rate of 40/h with a sample-to-wash ratio of 1/2, carryover is negligible, reproducibility is excellent, and 80% of steady state is achieved. Analytical recovery of added galactose was 95%. The method has the requisite sensitivity and accuracy for quantification of galactosemia and galactosuria in milkfed newborn infants and genetic evaluation of families of patients.

Glycogen metabolism in human skin fibroblasts. Influence of maltose on the activity of acid alpha-1, 4-glucosidase.

Maltose added to medium in a concentration of 100 mg/100 ml enhances the hydrolytic activity of acid alpha-1, 4-glucosidase in skin fibroblasts in culture derived from normal human subjects, but under the same conditions maltose has no demostrable effect on the enzyme in fibroblasts derived from skin of patients with Cori Type II glycogenosis. Upon addition of maltose to Cori Type II fibroblasts there is a marked decrease of glucose in medium overlying the cells with a concomitant marked increase in glycogen content of the same cells. Glycogen decreases in a similar manner in both normal and mutant cell types after 16 days in culture. This apparent utilization or degradation of glycogen in Cori Type II fibroblasts in culture is difficult to explain unless only a proportion of the polysaccharide accumulates within lysosomes. We propose, therefore, that extra-lysosomal glycogen which accumulates in fibroblasts from Cori Type II glycogenosis may be more easily degraded by glycogenolytic cytoplasmic enzymes, particularly in cells grown for as long as 2 wk in glucose-starved media.