J. F. Williams

Estimation of pentose 5-phosphate in the presence of heptulose and hexose phosphates by the orcinol method

Abstract 1. 1. The basic orcinol reaction with pentose, described by Mejbaum in 1939, has been modified. 2. 2. In the present method the temperature of the reaction has been reduced from 100° C to 50° C. This eliminates the reactivity of heptulose and hexose phosphates with the orcinol reagent. 3. 3. If the reaction time is extended to 2.5 hours at 50° C, ribose 5-phosphate only reacts to give 76–78 % of the maximum absorbance which is obtained by heating for 30 minutes at 100° C.

EXCHANGE REACTIONS IN METABOLISM

Abstract Recent studies from this laboratory [l, 2] on the reaction mechanism of the pentose phosphate pathway in rabbit and rat liver cells have accentuated the role of enzyme-catalyzed exchange reactions as a means by which tracer carbon is relocated in the absence of a net metabolic flux. While this is an intrinsic property of the group transferring enzymes of the pathway and is seen as a deleterious property of 14C for the mapping and quantitation of metabolic pathways, it has re-emphasized the possible usefulness of isotope exchange reactions in understanding the mechanism of action of natures catalyst.

Biochemical responses to hypoxia in the liver of the rabbit

Abstract 1. 1. Rabbit liver in situ was subjected to increasing periods of ischaemia by clamping the hepatic veins. 2. 2. Oxygen tension of blood retained in the liver was measured for periods of up to 15 minutes and the oxygen tension across liver cells was estimated during the different intervals of partial ischaemia. 3. 3. The [free NAD+]/[free NADH] ratios in both the mitochondrial and cytosolic compartments decreased during the period of partial ischaemia, as did the calculated adcnylate proportion ([ATP]/[ADP][HPO2−4]) of the cytosol. 4. 4. There was no increase in anaerobic glycolysis during the first 5 minutes of partial ischaemia. 5. 5. Glucose production by liver was maintained at a normal linear rate (1 μmole per minute per g. wet weight) in the 40-hour starved rabbit during 6 minutes of partial hepatic ischaemia.

Studies in situ on the effects of hyperglycemia on the C1/C6 ratio and the regulation of fatty acid metabolism in rabbit liver.

Abstract 1. 1. Using a technique which allows the study of liver metabolism in situ , acute changes in hepatic metabolism were examined following intravenous administration of glucose (0·2–1·6 g per animal) to 40-hr starved anaesthetized rabbits. 2. 2. Administration of 0·8 g of glucose resulted in a 2·5-fold decrease in the ratio: relative molar specific radioactivity of 14 CO 2 from the oxidation of [1- 14 C] glucose/ relative molar specific radioactivity of 14 CO 2 from the oxidation of [6- 14 C] glucose This ratio decreased from 11·7 at a blood glucose concentration of 82 mg % to 4·6 at 240 mg %, reflecting an overall decrease in the oxidation of [1- 14 C] glucose. 3. 3. In addition, glucose administration to the starved rabbit resulted in a threefold decrease in the amount of glucose released by the liver, a threefold increase in the hepatic concentration of long chain fatty acids and long chain fatty acyl CoA derivatives and a twofold increase in the hepatic concentration of Sn- glycero -3- phosphoric acid . 4. 4. It is concluded that glucose administration to the fasted animal depresses hepatic gluconeogenesis, fatty acid oxidation and redirects carbon flux to triglyceride synthesis.