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Biomedical subjects

J Stubbe

Publications and source records attributed to J Stubbe.

116 records · Page 7Linked to original sources
PubMed1981

On the mechanism of ribonucleoside triphosphate reductase from Lactobacillus leichmannii. Evidence for 3' C--H bond cleavage.

The 3' carbon-hydrogen bond of [3'-3H]uridine 5'-triphosphate is is cleaved during its conversion to 2'-deoxyuridine 5'-triphosphate catalyzed by Lactobacillus leichmannii ribonucleoside triphosphate reductase. A selection against 3H of approximately 1.8 is observed on this reduction. During the course of this reaction, no 3H is released to the solvent, and no 3H is recovered in reisolated coenzyme B12. Incubation of [3'-2H]uridine 5'-triphosphate with enzyme resulted in production of 2'-deoxy[3'-2H]uridine 5'-triphosphate.

Carbon Radioisotopes↗
PubMed1980

On the mechanism of ribonucleoside diphosphate reductase from Escherichia coli. Evidence for 3'-C--H bond cleavage.

The 3'-carbon--hydrogen bond of [3'-3H]uridine 5'-diphosphate is cleaved during its conversion to 2'-deoxyuridine 5'-diphosphate catalyzed by Esherichia coli ribonucleoside diphosphate reductase. A selection against 3H of approximately 3.3 is observed on this reduction reaction. During the course of this reaction, a small but significant amount of 3H is released to the solvent.

Carbon Radioisotopes↗
PubMed1980

Are carboxylations involving biotin concerted or nonconcerted?

Transcarboxylase and propionyl-CoA carboxylase catalyze the elimination of HF from beta-fluoropropionyl-CoA to form acrylyl-CoA. No carboxylation products of fluoropropionyl-CoA could be detected. The elimination proceeds at approximately the same rate as the normal carboxylation reactions. With propionyl-CoA carboxylase, ATP was required (HCO3- was also present) and was hydrolyzed to ADP and Pi. The rate of ADP formation was equal to that of acrylyl-CoA formation. A previous report (Stubbe, J. A., and Abeles, R. H. (1977) J. Biol. Chem. 252, 8338--8340) that acrylyl-CoA formation is faster than ADP formation is in error. With transcarboxylase, oxalacetate was required for acrylyl-CoA formation, and pyruvate was produced. The rate of pyruvate formation was equal to that of acrylyl-CoA formation. We conclude that the ability of the enzyme to catalyze the elimination of HF from beta-fluoropropionyl-CoA indicates that the enzyme can catalyze the abstraction of the substrate alpha-proton without concomitant carboxylation of the substrate. We also conclude that the normal catalytic reaction, therefore, probably involves a carbanion intermediate and does not proceed through a concerted process as has frequently been proposed.

Acyl Coenzyme A↗
PubMed1977

Biotin carboxylations--concerted or not concerted? That is the question!

When beta-fluoropropionyl coenzyme A is used as substrate, propionyl-CoA carboxylase catalyzes the formation of ADP and the elimination of fluoride ion. No F- release occurs in the absence of ATP or in the presence of avidin. ADP formation occurs as rapidly as in the presence of propionyl-CoA, but the rate of F- release is 6 times that of ADP formation. The rate of F- release is indicative of the minimal rate of abstraction of the alpha proton, and the rate of ADP formation is equivalent to the rate of formation of biotin-CO2. The results, therefore, show that hydrogen abstraction can occur without concomitant CO2 transfer from biotin-CO2 to the substrate. Therefore, the concerted mechanism which has been proposed for this, and other biotin enzymes, is not applicable when propionyl-CoA carboxylase acts on beta-fluoropropionyl-CoA. We believe the concerted mechanism is also not involved in the carboxylation of the normal substrate, propionyl-CoA.

Acyl Coenzyme A↗
PubMed1975

Chemical specificity of pyruvate kinase from yeast.

Three analogs of phosphoenolpyruvic acid: (Z)-phosphoenol-3-fluoropyruvate, (Z)-phosphoenol-3-bromopyruvate and (Z)-phosphoenol-alpha-ketobutyrate were found to be substrates for yeast pyruvate kinase (ATP: pyruvate (Z)-O-phosphotransferase, EC 2.7.1.40)with maximal velocities much greater than those found for rabbit muscle pyruvate kinase. The analogs exhibited sigmoidal kinetics, which become hyperbolic upon addition of the allosteric effector, fructose 1,6-diphosphate. Moreover, the reaction of (Z)-phosphoenol-3-bromopyruvate with ADP to produce bromopyruvic acid and ATP irreversibly inhibited the enzyme with a half-life of 32 min.

Adenosine Triphosphate↗
PubMedDate not supplied

Intratumoral steatosis in focal nodular hyperplasia coinciding with diffuse hepatic steatosis: CT and MRI findings with histologic correlation.

Focal nodular hyperplasia (FNH) is a benign tumorlike condition that is thought to be a hyperplastic response to increased blood flow in an arterial malformation rather than a true neoplasm. Radiologically, FNH usually shows typical findings on unenhanced and enhanced computed tomography (CT) and magnetic resonance images (MRI), with atypical features being the exception rather than the rule. We report an unusual case of FNH with extensive fatty infiltration of the lesion illustrated on CT and MRI and proven by histopathology.

Biopsy↗