Juvenile polysaccharidosis with cardioskeletal myopathy.

Polysaccharidoses with ultrastructural features reminiscent of glycogenosis type IV, but without enzymatic correlation, have been observed in several adolescent and adult patients. Little is known of the clinical, pathologic, or biochemical nature of these disorders. We describe a patient with ultrastructural characteristics consistent with glycogenosis type IV, but with normal brancher enzyme activity in dermal fibroblasts and cardiac muscle. During life and at autopsy, electron microscopy revealed amylopectin-like polysaccharide deposits present in a wide variety of tissues. The polysaccharidosis of our patient and similar patients may be a variant of glycogenosis type IV with a yet to be defined enzymatic defect.

Human phosphoribosylpyrophosphate synthetase: radioimmunochemical quantitation in erythrocytes and fibroblasts.

PRPP synthetase catalyzes the synthesis of PRPP, a regulatory substrate in the pathway of purine nucleotide synthesis de novo. We have developed a specific assay for quantitative determination of PRPP synthetase immunologically cross-reactive material in human erythrocyte and fibroblast extracts. The sensitivity of the radioimmunoassay (0.3% and 0.08% of normal mean cross-reactive material in erythrocytes and fibroblasts, respectively) was equivalent to that of the enzymatic activity assay, but enzyme protein initially present in relatively inactive monomeric and smaller aggregated forms was radioimmunochemically measurable. The radioimmunoassay was utilized in conjunction with the enzymatic assay to study normal PRPP synthetase and PRPP synthetases from five affected male patients (in four families) in whom inherited enzyme superactivity was associated with increased rates of PRPP and purine nucleotide synthesis and gout with excessive uric acid excretion. Despite increased enzymatic activities in patients' cell extracts, values for cross-reactive material were within the ranges measured in the respective normal cell extracts. Thus, calculated absolute specific activities (nmol/hr/mg cross-reactive material) of patients' PRPP synthetases were substantially greater than those of normal PRPP synthetase. Moreover, absolute specific activities in hemolysates from both patients and normal individuals were in close agreement with the enzyme-specific activities measured in preparations of erythrocyte PRPP synthetase purified to homogeneity from the corresponding patient or normal source. These findings provided evidence for the accuracy and specificity of the radioimmunoassay and supported previous evidence for increased maximal reaction velocity as the basis of superactivity of the patients' enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Gout with superactive phosphoribosylpyrophosphate synthetase due to increased enzyme catalytic rate.

We have studied families C and A in which superactivity of PRPP synthetase (E.C. 2.7.6.1) is associated with gout and uric acid overproduction in affected hemizygous males. PRPP synthetase catalyzes synthesis of PRPP, a regulatory substrate in purine synthesis de novo. Activities of the enzyme in erythrocyte and fibroblast extracts from the male index cases, T.C. and R.A., were nearly threefold greater than normal at each Pi concentration tested. PRPP synthetase superactivity was accompanied by increased intracellular PRPP concentration and generation in erythrocytes and fibroblasts from these patients, and enhanced rates of PRPP-dependent purine synthesis reactions, including purine synthesis de novo, were demonstrable in their fibroblasts. These findings suggested that increased intracellular synthesis dut to enzyme superactivity underlay purine nucleotide and uric acid overproduction in these patients. Similar studies in cells from the sister of T.C. and the mother of R.A. showed increased values that were, however, intermediate between normal values and those of the affected males, indicating that these women are heterozygous carriers of the traits for enzyme superactivity. The enzymatic basis for increased PRPP synthetase activity in both families was investigated. Immunochemical studies in dialyzed erythrocyte lysates and highly purified erythrocyte enzyme preparations provided evidence for increased enzyme activity per molecule of immunoreactive enzyme. In addition, purified T.C. and R.A. PRPP synthetases showed 3.1- and 2.8-fold greater enzyme specific activities, respectively, than comparably purified normal enzymes. Kinetic constants of purified T.C. and R.A. PRPP synthetases for substrates, activators, and inhibitors were indistinguishable from normal, and increased maximal reaction velocity alone appeared to account for enzyme superactivity. Despite an apparently similar kinetic mechanism for superactivity, the diminished electrophoretic mobility of T.C. PRPP synthetase and increased thermal lability of R.A. PRPP synthetase suggested distinct structural alterations leading to enzyme superactivity in families C and A.

Regional localization of the gene for human phosphoribosylpyrophosphate synthetase on the X chromosome.

Sixty-eight independent hybrid clones were isolated after irradiated normal human lymphocytes were fused with Chinese hamster fibroblasts lacking hypoxanthine-guanine phosphoribosyltransferase activity. The cells were grown under selective conditions requiring retention of the X chromosome-linked locus for human hypoxanthine-guanine phosphoribosyltransferase. The frequency and patterns of cotransference of human phosphoribosylpyrophosphate synthetase with the selected marker and with additional X-linked enzymatic markers confirm X linkage of the structural gene for human phosphoribosylpyrophosphate synthetase and support assignment of this gene to a position on the long arm of the X, between the loci for alpha-galactosidase and hypoxanthine-guanine phosphoribosyltransferase.