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Biomedical subjects

F B Rudolph

Publications and source records attributed to F B Rudolph.

At least 91 records · Page 5Linked to original sources
PubMed1977

Effect of CrATP on the association of the reacting forms of yeast hexokinase.

Reacting enzyme sedimentation studies have been performed with yeast hexokinase isozymes A and B in the presence and absence of chromium ATP at pH 6.75. Preincubation of either isozyme with CrATP causes a shift in the monomer-dimer equilibrium toward the monomeric form. The results are consistent with the observed increase in inhibition caused by CrATP (Danenberg, K.D., and Cleland, W.W. (1975) Biochemistry 14, 28-39) being due to a conformational change in the protein which causes a decrease in the association constant for the monomer.

Adenosine Triphosphate↗
PubMed1977

The catalytic activity of monomeric yeast hexokinase A.

It has been suggested [Williams, D.C. & Jones, J.G. (1976) Biochem. J. 155, 661-667] that monomeric hexokinase isoenzyme A is not catalytically active. We here present data from reacting-enzyme sedimentation, dissociation experiments and from previous studies which are consistent with the monomeric form possessing catalytic activity.

Catalysis↗
PubMed1977

Regulation of purine metabolism: a comparative study of the kinetic properties of adenylosuccinate synthetases from various sources.

1. Adenylosuccinate synthetase has been partially purified from rat liver, fetal rat liver, Novikoff ascites cells, Walker carcinoma 256 solid tumors, chicken liver and muscle, rabbit muscle and pig brain. 2. Considerable differences exist in Michaelis constants among the various species and the changes possibly reflect differences in regulation. 3. The kinetic properties of the enzyme are generally consistent with proposed metabolic roles in various tissues.

Adenylosuccinate Synthase↗
PubMed1976

Interaction of tetraiodofluorescein with yeast hexokinase.

The dye tetraiodofluorescein (TIF) was found to be an effective inhibitor of yeast hexokinase. It is a competitive inhibitor relative to MgATP2- and a noncompetitive inhibitor of glucose binding, a kinetic pattern consistent with the previously proposed random kinetic mechanism. TIF interacts directly with the native dimeric protein to give a difference spectrum with a maximum at 543 nm. Monomeric protein (produced by addition of 0.6 M NaCl) interacts with TIF to give a slightly altered difference spectrum, with the gammamax at 545 nm. The difference spectrum of the dimeric form is not perturbed by the addition of substrates but the absorbance with the monomer is lowered by MgATP2-. The Kd for MgATP2- was estimated to be 7 nM for monomeric hexokinase. These results suggest that results of previous binding studies with hexokinase at high concentrations which have been interpreted as being at variance with kinetic studies are due likely to different conformations of the protein under different experimental conditions.

Adenosine Triphosphate↗
PubMed1976

The kinetic mechanism of rat kidney gamma-glutamylcysteine synthetase.

A detailed kinetic investigation was made of the binding mechanism of gamma-glutamylcysteine synthetase purified from rat kidney. The results of initial rate and inhibition studies are consistent with a partially random mechanism in which ATP is the obligatory first substrate and both amino acids bind in a random order to the enzyme-ATP complex. Formation of the enzyme-substrate quaternary complex is necessary prior to release of products. This mechanism is consistent with previous binding studies with the enzyme and while it does not rule out participation of enzyme-bound gamma-glutamyl phosphate as an intermediate in catalysis, such an intermediate cannot be a discrete covalent complex.

Adenosine Diphosphate↗
PubMed1976

Regulation of purine metabolism. Adenylosuccinate synthetase from Novikoff ascites tumor cells.

Adenylosuccinate synthetase has been partially purified from Novikoff ascites tumor cells. The properties of the protein are quite different from the enzyme from rat liver in that the Km for asparate is higher and the K1 for the feedback inhibitor AMP is also higher. The antibiotic hadacidin has a preferential inhibitory effect on the tumor enzyme. These results suggest that the Novikoff ascites tumor enzyme is less sensitive to normal feedback controls but may be more sensitive to specific antitumor drugs.

Adenosine Monophosphate↗
PubMed1976

Rat liver pyruvate carboxylase. Inhibition by chromium nucleotide complexes.

The effect of inert coordination complexes of chromium (III) with various nucleotides on the catalytic activity of rat liver pyruvate carboxylase was determined. The chromium nucleotides are effective initial inhibitors of pyruvate carboxylase and the inhibition becomes more severe with time. The initial rate decreases for several minutes, reaching a new slower rate that is then maintained until considerable net reaction occurs. Incubation of the enzyme with chromium nucleotides in the presence of Mg2+ and HCO3- causes maximal inhibition of the reaction and linear initial rates are then observed. This effect is similar to that found with yeast hexokinase (Dannenberg, K.D., and Cleland, W.W. (1975) Biochemistry 14, 28-39). The specificity of the carboxylase toward the nucleotide complexes suggests that the alpha and beta nucleotide phosphates are as important as the gamma phosphate in binding to the enzyme. A stable pyruvate carboxylase chromium nucleotide complex was not observed. These results are quite different from those found with yeast hexokinase where a stable complex between CrATP, sugar, and enzyme is found and hexokinase appears to be specific toward the beta, gamma phosphates of its nucleotide substrates.

Adenosine Diphosphate↗
PubMed1975

Rat liver pyruvate carboxylase. V. Reversible dissociation by chloride salts of monovalent cations.

Rat liver mitochondrial pyruvate carboxylase is inactivated reversibly and converted to protomers by incubation at 0 degrees in the presence of high concentrations of Cl- salts of monovalent cations. This inactivation, as well as restoration of enzymic activity, is dependent on temperature, protein concentration, and salt concentration. MgCl2 or sucrose are relatively effective in preventing inactivation and are required along with EDTA for reactivation. The enzyme can be dissociated reversibly from the native tetramer into enzymically active dimers and protomers by incubation with 30 to 100 mM ammonium chloride at 0 degrees and pH 7.0 Isolated monomeric enzyme is activated by acetyl-CoA and appears to show sigmoid saturation curves with respect to acetyl-CoA binding. Biphasic double reciprocal plots are obtained with respect to pyruvate as previously shown for the tetramer.

Acetyl Coenzyme A↗