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R I Feldman

Publications and source records attributed to R I Feldman.

28 records · Page 2Linked to original sources
PubMed1985

Membrane-specific inhibitors of the bovine heart mitochondrial ATPase.

New cationic inhibitors of the bovine heart mitochondrial ATPase have been synthesized by quaternizing 1-dansylamido-3-dimethypropylamine with decyl and hexadecyl iodides. These ligands are unique in their mode of action because they inhibit the submitochondrial membrane-associated forms of the enzyme more potently than the soluble form of the enzyme (F1). Derivatives prepared with propyl or hexyl iodides are weak inhibitors and exhibit little affinity for submitochondrial membranes particle. The inhibitory effectiveness of these derivatives measured either in the direction of ATP synthesis or ATP hydrolysis results from efficient insertion into the membrane. Other inhibitory organic cations such as the 3:1 4,7-diphenyl-1,10-phenanthroline-ferrous chelate and alkyl guanidines inhibit both the membrane-associated and soluble ATPase comparably.

Adenosine Triphosphatases↗
PubMed1984

Enzymatic activities in thylakoid membranes, which form medium [32P]NDP and [32P]ATP from 32Pi. Polynucleotide phosphorylase and adenylate kinase.

Soluble chloroplast coupling factor 1 (CF1) and the ATP synthase complex, under uncoupled conditions, can form bound ATP from tightly bound ADP and medium Pi. This partial reaction is a powerful probe of the mechanism of ATP synthesis. During our study of the synthesis of bound ATP by CF1 other enzyme activities, which generate [32P]nucleotides from 32Pi, were characterized and controlled. Two enzymes present at significant levels in the preparations are polynucleotide phosphorylase and adenylate kinase. Polynucleotide phosphorylase (PNPase) was found both in thylakoid and CF1 preparations and catalyzed the formation of [beta-32P]ADP via its Pi----ADP exchange activity. The formation of [beta-32P]ADP during net photophosphorylation is attributable to adenylate kinase action on the [32P]ATP formed since hexokinase and glucose effectively block its production. In addition, PNPase also degraded RNA present in thylakoid preparations yielding all four [32P]nucleoside diphosphates. PNPase was also shown to catalyze a Pi----ATP exchange that is dependent on RNA primers and other cofactors.

ATP Synthetase Complexes↗
PubMed1983

The synthesis of ATP by the membrane-bound ATP synthase complex from medium 32Pi under completely uncoupled conditions.

Previously, we demonstrated that isolated coupling factor 1 can reversibly synthesize bound ATP from "tightly bound" ADP and medium Pi (Feldman, R I., and Sigman, D. S. (1982) J. Biol. Chem. 25, 1676-1683). In order to ensure that the thermodynamic constants derived are relevant to coupled ATP synthesis, we have also studied the reaction on thylakoid membranes. The ATP synthase complex, uncoupled with 20 mM NH4Cl or 0.3% Triton X-100, synthesizes enzyme-bound ATP in a similar manner to coupling factor 1. The pH optimum is 6, the concentration of medium Pi for 50% saturation is 38 mM, and the equilibrium constant for the formation of ATP from bound ADP and Pi is 0.5. It is concluded that the active site responsible for the reaction is not appreciably altered by the dissociation of coupling factor 1 from the membrane or Fo. Thus, either enzyme form can be used to derive data relevant to the mechanism of ATP synthesis. The ability to measure bound ATP synthesis in an energizable system will allow us to probe the effect of membrane energization on the accumulated bound product.

ATP Synthetase Complexes↗
PubMed1982

The synthesis of enzyme-bound ATP by soluble chloroplast coupling factor 1.

Purified CF1 (chloroplast coupling factor 1) synthesizes enzyme-bound ATP (CF1 less than ATP) from medium Pi. The reaction does not depend on medium ADP, indicating that the ADP substrate is tightly bound to CF1 (CF1 less than ADP). At saturating [Pi] and at the pH optimum of 6.0, a yield of 0.25 mol of ATP/mol of CF1 was obtained. The addition of hexokinase and glucose does not reduce the yield of CF1 less than ATP, showing that the ATP is never released from the enzyme. The addition of medium ATP, but not ADP, promotes the hydrolysis of CF1 less than ATP. The formation of CF1 less than ATP was analyzed in terms of a two-step reaction sequence in which Pi first binds to CF1 less than ADP which is then converted to CF1 less than ATP. Acid pH values were shown to increase the yield of CF1 less than ATP most significantly by promoting Pi binding. The equilibrium constant for the conversion of CF1 less than ADP . Pi to CF1 less than ATP was the same (0.4 at pH 6.0 and 7.0. The data suggest that acid pH values stimulate Pi binding by increasing the concentration of the H2PO4- species, which has been previously shown to be the form of phosphate that binds to beef heart F1 (33). These studies provide another example of an enzyme that dramatically lowers the free energy difference between enzyme-bound reactants and products compared to that of the same reaction occurring free in solution. The formation of CF1 less than ATP, if at the active site of photophosphorylation, means that protonmotive force does not directly promote the synthesis of the beta-gamma phosphoryl bond of ATP during energy-driven ATP synthesis.

Adenosine Diphosphate↗
PubMed1977

Hemagglutination inhibition assay for gentamicin.

A rapid and simple hemagglutination inhibition test for measuring gentamicin concentrations in serum has been developed. Correlation coefficients for this assay with the radioimmunoassay and microbiological assay were r = 710 and r = 0.864, respectively. Measurements of gentamicin levels in serum by the three methods showed no statistically significant differences. The hemagglutination inhibition assay is fast, reliable, and relatively inexpensive, and should prove valuable for laboratory use.

Biological Assay↗
PubMed1975

Purine mutants of mammalian cell lines. II. Identification of a phosphoribosylpyrophosphate amidotransferase-deficient mutant of Chinese hamster lung cells.

A class of purine auxotrophs blocked early in the purine biosynthetic pathway was examined. The inability of these mutants to accumulate formylglycinamide ribotide (FGAR) in the presence of azaserine suggested that one or more of the first three enzymes of the pathway were either missing or defective. By direct enzyme assay, phosphoribosylpyrophosphate (PRPP) amidotransferase (E.C. 2.4.2.14) was found to be absent in extracts of mutant cells. Thus these cells were unable to convert PRPP to phosphoribosylamine (PRA). By reacting ribose 5-phosphate with ammonium ions, PRA was generated nonenzymatically in the incubation mixture, thus enabling us to test for the presence of the two enzymes required to convert PRA to FGAR. It was demonstrated that sufficient amounts of these enzymes, phosphoribosylglycineamide synthetase (E.C. 6.3.1.3) and phosphoribosylglycineamide formyltransferase (E.C. 2.1.2.2), were present in mutant extracts to allow synthesis of FGAR to occur once PRA was so provided.

Adenine↗
PubMedDate not supplied

Tracheotomies: a 10-year experience in 319 children.

A retrospective analysis was made of 319 patients having tracheotomies at the Hospital for Sick Children in Toronto between 1976 and 1985. In comparison to a similar study at the same institution completed 15 years earlier, the average number of tracheotomies per year has declined by half, because almost no tracheotomies are now done in patients with epiglottitis and tracheitis. Tracheotomies for children with CNS disorders and craniofacial anomalies are relatively more frequent. The average duration of tracheotomy is almost 1 year (339 days). Complications occurred in 30% of patients, but tracheotomy-related mortality was less than 1%.

Adolescent↗