Search PubMed⌕ Search

Biomedical subjects

I H Fox

Publications and source records attributed to I H Fox.

At least 145 records · Page 8Linked to original sources
PubMed1976

Purine catabolism in man: characterization of placental microsomal 5'-nucleotidase.

Human placental microsomal 5'-nucleotidase (EC 3.1.3.5) was prepared free of alkaline phosphatase by isoelectric focusing. A total of seven electrophoretic variants were isolated during the preparation of six placentas. Only three to six variants were found in a single placenta. The isoelectric pH's were 6.70, 6.44, 6.23, 6.02, 5.76, 5.63 and 5.44. These were found to be composed of variable quantities of a large, medium and low molecular weight form. The apparent molecular weights of the medium and light form of the enzyme were 86 500 and 43 500, respectively, as estimated from Stokes radius and sedimentation velocity determinations. The electrophoretic variants were not distinguishable with respect to specific activity and Michaelis constants for AMP, GMP or CMP or inhibition by ATP, CTP or adenosine. These electrophoretic variants appeared to be pseudoisozymes based upon different states of aggregation of a common primary sequence. There was a wide range of substrate specificity among nucleoside 5'-monophosphates which included 2-deoxyribose compounds. With AMP as 100, substrate activity was: CMP, 122; NMN, 74; GMP, 68: IMP, 63; XMP, 28 and UDP-glucose, 68. The Michaelis constants for AMP, GMP and CMP ranged from 12-18 muM, from 33-67 muM and from 170-250 muM, respectively. Although 5'-nucleotidase was active in the absence of divalent cation, 5 mM MgCl2 stimulated the enzyme activity to 234% of control and shifted the pH optimum of 9.8 to a plateau from pH 7.4-9.8.

Cations, Divalent↗
PubMed1976

Purine catabolism in man: inhibition of 5'-phosphomonesterase activities from placental microsomes.

The 5'-phosphomonoesterase activity of 5'-nucleotidase (EC 3.1.3.5) and alkaline phosphatase (EC 3.1.3.5) participates in the catabolism of purine ribonucleotides to uric acid in humans. Initial velocity studies of 5'-nucleotidase suggest a sequential mechanism of interaction between AMP nad MgCl2, with a Km of 14 and 3 muM, respectively. With product inhibition studies the apparent Ki's for adenosine, inosine, cytidine, and inorganic phosphate were 0.4, 3.0, 5.0, and 42 mM, respectively. A large number of nucleoside mono-, di-, and tri-phosphate compounds were inhibitors of the enzyme. Allopurinol ribonucleotide, ADP, or ATP were competitive inhititors when AMP was the substrate, with a Ki slope of 120 muM. The phosphomonoesterase activity of human placental microsomal alkaline phosphatase had a pH optimum of 10.0 and had only 18% of maximum activity at pH 7.4. Substrates and inhibitors included almost any phosphorylated compound. The Km for AMP was 0.4 mM and the apparent Ki for Pi was 0.6 mM. Activity was increased only 19% by 5 mM MgCl2. These observations suggest that 5'-nucleotidase and alkaline phosphatase may be inhibited by ATP and Pi, respectively, under normal intracellular conditions, and that AMP may be preferentially hydrolyzed by 5'-nucleotidase.

Alkaline Phosphatase↗
PubMed1976

Ascorbic acid-induced uricosuria. A consequency of megavitamin therapy.

The effect of ascorbic acid on the serum and urinary uric acid was studied in 14 subjects. Two to 6 h after the ingestion of 4.0 g of ascorbic acid, the fractional clearance of uric acid increased to 202% +/- 41% of the control value. This uricosuria was inhibited by pyrazinamide and by low-dose acetylsalicylic acid, but was not accompanied by an increase of the creatinine clearnace. Ascorbic acid did not diminish protein-bound uric acid. In 3 subjects who ingested 8.0 g of ascorbic acid for 3 to 7 days the serum uric acid decreased by 1.2 to 3.1 mg/dl as a result of a sustained uricosuria. These results suggest that ascorbic acid could invalidate studies involving the measurement of uric acid and obscure the diagnosis of gout in some cases. Theoretically it could precipitate attacks of gouty arthritis or renal calculi in predisposed persons. These observations show a pharmacologic effect of megadoses of a simple vitamin.

Ascorbic Acid↗
PubMed1975

Mechanism for the paradoxical aciduria following alkali administration to prolonged-fasted patients.

Rapidly induced systemic alkalinization due to either sodium-lactate or sodium-bicarbonate infusion in prolonged-fasted subjects with steady-state ketoacidosis was associated with a decrease in urine pH. This decrease in urine pH from 5.50 to 5.20 was the result of a significant decrease in urinary ammonium excretion from 8.40 to 6.35 mEg/hr and was not accompanied by an increase in net acid excretion (11.3 vs. 10.6 mEg/hr). The decreased ammonium excretion is attributed to the raised pH of the proximal tubular fluid resulting in a less favorable pH gradient for gaseous ammonia entry. This would decrease gaseous ammonia generated in the loop of Henle for collecting duct buffering of secreted hydrogen ions.

Acidosis↗
PubMed1975

Hypoxanthine-guanine phosphoribosyltransferase. Characterization of a mutant in a patient with gout.

The mutation in a young gouty male with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase has been evaluated. The serum uric acid was 11.8 mg/100 ml, and the urinary uric acid excretion was 1,279 mg/24 h. Erythrocyte hypoxanthine-guanine phosphoribosyltransferase was 34.2 nmol/h/mg, adenine phosphoribosyltransferase was 36.5 nmol/h/mg and phosphoribosylpyrophosphate was 2.6 muM. Hypoxanthine-guanine phosphoribosyltransferase from peripheral leukocytes and cultured diploid skin fibroblasts was within the normal range, but enzyme activity in rectal mucosa was below the normal range. Initial velocity studies of the normal enzyme and the mutant enzyme from erythrocytes with the substrates hypoxanthine, guanine, or phosphoribosylpyrophosphate showed that the Michaelis constants were similar. Product inhibition studies distinguished the mutant enzyme from the normal enzyme. Hyperbolic kinetics with increasing phosphoribosylpyrophosphate were converted to sigmoid kinetics by 0.2 mM GMP with the mutant enzyme but not with the normal enzyme. The mutant erythrocyte hypoxanthine-guanine phosphoribosyltransferase was inactivated normally at 80 degrees C and had a normal half-life in the peripheral circulation. The mol wt of 48,000 was similar to the normal enzyme mol wt of 47,000. With isoelectric focusing, the mutant erythrocyte enzyme had two major peaks with isoelectric pH's of 5.50 and 5.70, in contrast to the isoelectric pH's of 5.76, 5.82, and 6.02 of the normal isozymes. Isoelectric focusing of leukocyte extracts from the patient revealed the presence of the mutant enzyme. Cultured diploid fibroblasts from the propositus appeared to function normally, as shown by the inability to grow in 50-100 muM azaguanine and by the normal incorporation of [14C]hypoxanthine into nucleic acid. In contrast, erythrocytes from the patient displayed abnormal properties, including the increased synthesis of phosphoribosylphyrophosphate and elevated functional activity of orotate phosphoribosyltransferase and orotidylic decarboxylase. These unique kinetic, physical, and functional properties provide support for heterogeneous structural gene mutations in partial deficiencies of hypoxanthine-guanine phosphoribosyltransferase.

Adult↗
PubMed1975

Inhibition of mitogen mediated lymphocyte blastogenesis by adenosine.

The effect of adenosine on the proliferative response of human peripheral circulating lymphocytes to stimulation by concanavalin A, phytohemagglutinin and pokeweed mitogen was evaluated. Increasing concentrations of adenosine substantially inhibited mitogen mediated lymphocyte blastogenesis. Erythro-9(2-hydroxyl-3-nonyl) adenine. HCl enhanced the inhibitory effect of adenosine. Inosine, the deamination product of adenosine, had an inhibitory effect which was less than that of adenosine. Inhibition by adenosine may be relevant to the normal regulation of immune function and may account in part for the pathophysiological relationship between severe combined immunodeficiency disease and adenosine deaminase deficiency.

Adenine↗
PubMed1975

The pharmacology of hypouricemic effect of benzbromarone.

The hypouricemic effect of benzbromarone has been investigated in six subjects. Benzbromarone increased urate: creatinine by 371 per cent over control values at two to four hours after administration. Over a 24 hour period, the mean serum uric acid decreased from a control value of 7.8 +/- 0.8 to 4.3 +/- 0.6 mg/dl. This uricosuric effect was completely reversed by pyrazinamide, partially inhibited by acetylsalicyclic acid and sulfinpyrazone, and was not accompanied by an elevation of the creatinine clearance or an inhibition of urate binding to plasma protein. In vitro studies showed only 22 per cent inhibition of urate binding by benzbromarone five muM, a concentration which is transiently reached in man. Kinetic studies of human liver xanthine oxidase demonstrated non-competitive inhibition with variable hypoxanthine and a Ki slope of 8.5 muM. The Ki slopes for benzarone and allopurinol were 19.0 muM and 0.05 muM respectively. There was no elevation of the urinary oxypurines following benzbromarone ingestion. These observations suggest that only the renal tubular activity of benzbromarone is relevant to its hypouricemic effects in man. (J Rheumatol 2: 437-445, 1975).

Adult↗