PubMed Health⌕ Search

Biomedical subjects

K G Rienits

Publications and source records attributed to K G Rienits.

13 recordsLinked to original sources
PubMed1986

The metabolic significance of pentose cycle measurements in perfused liver.

The controversial dissension concerning the nature of the pentose cycle in liver is investigated. The metabolism of [2-14C]Glc and [1-14C]Rib in chronically perfused normal and regenerating rabbit liver and acutely perfused rat liver are used to test the mechanistic predictions and contribution of the F-type pentose cycle. 14C was traced in Glc, Glc 6-P, Fru 6-P, glycogen and Rib 5-P. None of the data complied with the critical theoretical limits set for the C-1/C-3 ratio (the identity badge of the F-type pentose cycle or pathway) for all values of F-type PC from 0-100%. Thus apparent F-type PC measurements using the Katz & Wood method gave a wide scatter of calculated values. The 14C distributions in Rib 5-P do not conform with the predictions of the F-type PC but are in agreement with the many previous results of similar experiments reported by Hiatt and co-workers. In perfused rat liver the C-1/C-3 constants in Glc 6-P and glycogen also failed to conform with F-PC theory following the metabolism of [2-14C]Glc. The metabolism of [5-14C]Glc and distribution of 14C in Glc 6-P and glycogen showed that L-type PC was 18%, in close agreement with a previous published value of 22% for rat hepatocytes. Metabolism of [6-14C]Glc and [4-14C]Glc (as [4,5,6-14C]Glc) showed that Pyruvate Recycling was active in perfused rat liver. None of the data from these comprehensive investigations can confirm the results of the recent study reported by the Landau laboratory on the pentose pathway metabolism of Glc and Rib in perfused rat liver.

Animals↗
PubMed1971

A system for the study in situ of the pentose phosphate pathway in rabbit liver.

A surgical procedure for the isolation of the liver from the systemic circulation of the anaesthetized rabbit is described. The technique allowed the metabolism in situ of intraportally infused substrates to be followed for periods up to 5min, free from the contaminating influences of metabolism by other body tissues. Details of the procedures necessary to achieve the uniform infusion, homogeneous distribution and containment of (14)C-labelled glucose substrates in the liver by haemostasis are described. Changes in pO(2), pCO(2), pH and the concentrations of NADP(+), NADPH and glucose during each minute interval of the total 5min period of metabolism are given. Reactant ratios of the lactate dehydrogenase system and the adenine nucleotide system have been calculated from the concentrations of the pertinent metabolites for the same period of metabolism. Glucose production by rabbit liver in situ proceeded at the rate of 1.08mumol/min per g wet wt. of liver during the 5min metabolic interval. The presence of the oxidative reactions of the pentose phosphate pathway of glucose metabolism was inferred from the quotient oxidation of [1-(14)C]glucose/oxidation of [6-(14)C]glucose=1.8.

Adenine Nucleotides↗
PubMed1971

The pentose phosphate pathway in rabbit liver. Studies on the metabolic sequence and quantitative role of the pentose phosphate cycle by using a system in situ.

1. The reactions of the pentose phosphate cycle were investigated by the intraportal infusion of specifically labelled [(14)C]glucose or [(14)C]ribose into the liver of the anaesthetized rabbit. The sugars were confined in the liver by haemostasis and metabolism was allowed to proceed for periods up to 5min. Metabolism was assessed by measuring the rate of change of the specific radioactivity of CO(2), the carbon atoms of glucose 6-phosphate, fructose 6-phosphate and tissue glucose. 2. The quotient oxidation of [1-(14)C]glucose/oxidation of [6-(14)C]glucose as measured by the incorporation into respiratory CO(2) was greater than 1.0 during most of the time-course and increased to a maximum of 3.1 but was found to decrease markedly upon application of a glucose load. 3. The estimate of the pentose phosphate cycle from C-1/C-2 ratios generally increased during the time-course, whereas the estimate of the pentose phosphate cycle from C-3/C-2 ratios varied depending on whether the ratios were measured in glucose or hexose 6-phosphates. 4. The distribution of (14)C in hexose 6-phosphate after the metabolism of [1-(14)C]ribose showed that 65-95% of the label was in C-1 and was concluded to have been the result of a rapidly acting transketolase exchange reaction. 5. Transaldolase exchange reactions catalysed extensive transfer of (14)C from [2-(14)C]glucose into C-5 of the hexose 6-phosphates during the entire time-course. The high concentration of label in C-4, C-5 and C-6 of the hexose 6-phosphates was not seen in tissue glucose in spite of an unchanging rate of glucose production during the time-course. 6. It is concluded that the reaction sequences catalysed by the pentose phosphate pathway enzymes do not constitute a formal metabolic cycle in intact liver, neither do they allow the definition of a fixed stoicheiometry for the dissimilation of glucose.

Acetates↗