Frederick M. Rosenbloom

Enzyme Defect Associated with a Sex-Linked Human Neurological Disorder and Excessive Purine Synthesis

A sex-linked familial neurological disease consisting of cerebral palsy, mental retardation, choreoathetosis, and compulsive aggressive behavior is associated with a loss of an enzyme that participates in purine metabolism, namely, hypoxanthine-guanine phosphoribosyltransferase. The production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis. This is the first example of a relation between a specific enzyme defect and abnormal compulsive behavior. It is also the first enzyme defect in purine metabolism demonstrated in a neurological disease.

Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency in Gout

Excerpt INTRODUCTION Sophisticated biochemical studies in recent years have revealed that the regulation of intracellular metabolism is a logical, orderly, and intricate process. Control of enzyme ...

Adenine phosphoribosyltransferase deficiency: a previously undescribed genetic defect in man

A deficiency of adenine phosphoribosyltransferase (A-PRTase) is described in four members in three generations of one family. A-PRTase is coded by an autosome and the mutants described in this report are heterozygotes for this enzyme defect. The level of enzyme activity in these heterozygotes was inappropriately low, ranging from 21 to 37% of normal rather than the expected 50% of normal. Examination of various physical and chemical properties of the A-PRTase obtained from the mutant heterozygotes failed to reveal differences from the normal enzyme. These patients have no discernable abnormality in uric acid production despite the finding that patients with a deficiency of a closely related enzyme, hypoxanthine-guanine phosphoribosyltransferase, invariably produce excessive quantities of uric acid. A relationship of the A-PRTase deficiency to the disturbance in lipoprotein metabolism observed in the propositus has not been firmly established. Possible manifestations of the homozygous form of this enzyme deficiency will require identification of such individuals in the future.

Increased free-cystine content of fibroblasts cultured from patients with cystinosis

The presence of a significantly increased content of free-cystine in skin fibroblasts from both homozygotes and heterozygotes for cystinosis emphasizes the central role of cystine in this disease, even though the primary defect responsible for cystine accumulation is yet to be determined. The studies described in this communication provide evidence that cystine is compartmentalized in a subcellular location in cystinotic cells. In fact, the very growth of cystinotic fibroblasts in the presence more than 100 times the usual content of free-cystine is evidence that the accumulated cystine is not freely dispersed throughout the cell, since would otherwise inhibit many enzymes requiring free sulfhydryl groups for activity (Patrick, 1965). We have no evidence as to whether the cystine is located in a known subcellular organelle or in a previously unrecognized location. Skin fibroblasts may provide a convenient tool to pursue these questions.

An enzymatic basis for variation in response to allopurinol. Hypoxanthine-guanine phosphoribosyltransferase deficiency.

Abstract Although allopurinol appears to decrease the rate of de novo purine biosynthesis, this effect is variable in gout, possibly because uric acid production is increased in patients who are relatively deficient in hypoxanthine-guanine phosphoribosyltransferase (HG-PRTase). To test this possibility, allopurinol was given to 11 patients with excessive uric acid production. In seven allopurinol had no effect on total excretion of purine catabolites. The same seven had a marked decrease in the activity of HG-PRTase and were also resistant to the effects of allopurinol on purine synthesis. These observations suggest that HG-PRTase activity is necessary for allopurinol to suppress purine synthesis de novo in man. This effect of allopurinol was also absent in four additional gouty patients with normal uric acid production and normal HG-PRTase activity. Hence, deficiency of this enzyme does not account for all cases of resistance to suppression of de novo purine biosynthesis by allopurinol.

Effects of orotic acid on purine and lipoprotein metabolism in man

Abstract In the present study, it was demonstrated that orotic acid, a normal intermediate in pyrimidine synthesis, inhibits purine biosynthesis de novo in normal man. This was associated with depletion of erythrocyte 5-phosphoribosyl-1-pyrophosphate (PP-ribose-P) content. Orotic acid had no inhibitory effect on purine biosynthesis in patients who exhibited elevated levels of PP-ribose-P due to a deficiency of hypoxanthine-guanine phosphoribosyltransferase. These findings suggest that the inhibitory effect of orotic acid on purine biosynthesis de novo is due to depletion of intracellular PP-ribose-P levels. This provides the first in vivo evidence that the physiologic intracellular concentration of PP-ribose-P is important for the regulation of purine biosynthesis de novo in man. Orotic acid administration also produced a modest though statistically significant decrease in the plasma concentration of cholesterol, triglycerides, and beta and prebeta lipoproteins. The uricosuric effect of orotic acid noted previously after its intravenous administration was confirmed in the present study in which the compound was administered orally.

The Effects of Azathioprine (Imuran) on Purine Synthesis in Clinical Disorders of Purine Metabolism

Azathioprine, a purine analogue, significantly suppressed the purine synthesis de novo of two gouty patients manifesting overproduction of uric acid, as well as three of four gouty patients who showed normal uric acid production. This suppression is taken as evidence that phosphoribosyl-pyrophosphate amidotransferase, the rate-controlling step in purine synthesis de novo, has a normal sensitivity to feedback inhibitors in the patients who responded to the drug.Two children afflicted with the familial disorder of hyperuricemia, choreo-athetosis, and self-mutilation described by Lesch and Nyhan showed no reduction in the activity of the biosynthetic pathway in response to azathioprine. This inability to respond to azathioprine can be directly related to the absence in these patients of the enzyme hypoxanthine-guanine phosphoribosyltransferase which is required for conversion of the drug or its metabolites to the biochemically active ribonucleotide form.

Variations in purine metabolism of cultured skin fibroblasts from patients with gout

Purine metabolism was studied in fibroblasts cultured from three patients with gout in an attempt to determine the biochemical bases of their disease. The rate of purine biosynthesis de novo was normal in one line of cells, but the rate of catabolism of adenine nucleotides to hypoxanthine and inosine was greatly increased. The rate of purine biosynthesis de novo was increased in two lines of cells, and this was associated with increased concentrations of 5-phosphoribosyl 1-pyrophosphate. Purine synthesis was also less sensitive than normal to feedback inhibition. The catabolism of inosinate synthesized de novo was increased.