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J T Tildon

Publications and source records attributed to J T Tildon.

At least 73 records · Page 4Linked to original sources
PubMed1980

Glycerol oxidation in rat brain: subcellular localization and kinetic characteristics.

The oxidation of [1,3-14C] glycerol to 14CO was measured in slices, whole homogenates, and subcellular fractions of rat brain. In all of these tissue preparations, the Lineweaver-Burk plots of glycerol oxidation were biphasic, yielding two apparent Km and V values. Similar kinetic characteristics were obtained with brain homogenates from guinea pig, mouse, rabbit, monkey, and pig. In other tissues of the rat, including heart, kidney, liver, and skeletal muscle, the Lineweaver-Burk plots for glycerol oxidation were not biphasic but were linear. Heating the brain homogenates for five minutes at 5 degrees C caused a 50% decrease in the rate of oxidation of glycerol without a change in the biphasic double reciprocal plot. The addition of purified glycerol kinase (EC 2.7.1.30) to the homogenate caused an increase in the rate of oxidation and resulted in linear Lineweaver-Burke plot. Brain mitochondria were prepared by two different methods, both of which yielded an enrichment of glycerol oxidation. In contrast, the rate of glucose oxidation was higher in homogenates than in mitochondria, and glucose competed with glycerol as substrate only extramitochondrially. The effects of various metabolic inhibitors suggested the participation of intact, coupled mitochondria, of glycolytic enzymes, and of electron transport in the oxidation of glycerol. The data support the primary localization of glycerol oxidation in nonsynaptic mitochondria in brain and the presence in that organelle of enzymes of the Embden-Meyerhoff pathway or an as yet unidentified system for oxidizing this compound.

Animals↗
PubMed1978

Effect of L-alanine infusion on gluconeogenesis and ketogenesis in the rat in vivo.

1. In 48 h-starved 6-week-old rats the 14C incorporation in vivo into blood glucose from a constant-specific-radioactivity pool of circulating [14c]actateconfirmed that lactate is the preferred gluconeogenic substrate. 2. Increasing the blood [alanine] to that occurrring in the fed state increased 14C incorporation into blood glucose 2.3-fold from [14c]alanine and 1.7-fold from [14c]lactate. 3. When the blood [alanine] was increased to that in the fed state, the 14C incorporation into liver glycogen from circulating [14c]alanine or [14c]lactate increased 13.5- and 1.7-fold respectively. 4. The incorporation of 14C into blood acetoacetate and 3-hydroxybutyrate from a constant-specific-radioactivity pool of circulating [14c]oleate was virtually abolished by increasing the blood [alanine] to that existing in the fed state. However, the [acetoacetate] remained unchanged, whereas [3-hydroxybutyrate] decreased, although less rapidly than did its radiochemical concentration. 5. It is concluded that during starvation in 6-week-old rats, the blood [alanine] appears to influence ketogenesis for circulating unesterfied fatty acids and inversely affects gluconeogenesis from either lactate or alanine. A different pattern of gluconeogenesis may exist for alanine and lactate as evidenced by comparative 14C incorporation into liver glycogen and blood glucose.

Acetoacetates↗
PubMed1978

Reciprocal regulation of glucose and glutamine utilization by cultured human diploid fibroblasts.

Human diploid fibroblasts utilize both glucose and glutamine as energy sources. The utilization of glutamine by fibroblasts is regulated by glucose, and vice versa. This conclusion is supported by the following observations: (1) essentially identical growth rates were observed in Eagle's minimum essential medium (MEM)3 in which the glucose concentration was either 5.5 mM or was maintained between 25 and 40 micrometer, (2) the total glutamine utilization by fibroblasts increase at least 30% in medium with 25 micrometer to 70 micrometer glucose compared to medium with 5.5 mM glucose, while the rate of glutamine-1 or 5-14C oxidation to CO2 increased 5-fold as the glucose concentration was decreased to zero, (3) 2 mM glutamine inhibited glucose-6-14C oxidation by 88% and stimulated glucose-1-14C by 77% in log phase cells and (4) glutamine oxidation in normal medium contributed approximately 30% of the energy requirement of human diploid fibroblasts.

Cell Division↗
PubMed1977

Hypoketonaemic effect of L-alamine. Specific decrease in blood concentrations of 3-hydroxybutyrate in the rat.

1. The injection of L-alanine (50-100 mg/kg) into 35-day-old rats that had been starveed for 48 h increased blood L-alanine concentration to values observed in fed animals and lowered the blood concentration of 3-hydroxybutyrate within 2 min. 2. This hypoketon aemic action of L-alanine was specific for 3-hydroxybutyrate, since the acetoacetate concentrations did not change significantly. 3. The decrease in 3-hydroxybutyrate elicited by L-alanine was not related to changes in the blood concentrations of insulin, glucagon, growth hormone, glucose, unesterified fatty acids, lactate or pyruvate. 4. The injection of L-alanine resulted in a decrease in total ketones that was apparently unrelated to their increased peripheral utilization. These results are interpreted as an anti-ketogenic action of L-alanine. 5. The data suggest that L-alamine lowers ketone-body formation in starved rats, possibly via an alteration in hepatic redox equilibrium.

Acetates↗
PubMed1977

Effects of starvation and development on mitochondrial acetoacetyl-coenzyme A thiolase of rat liver.

The activity of the putative ketogenic beta-oxoacyl-CoA thiolase from mitochondria of rat liver increases with starvation, during neonatal life, and after the injection of glucagon. These changes are associated with alteration in ketonaemia. The changes in activities of this species of thiolase are not associated with significant alterations in the apparent affinity (Km) for the ketogenic substrate, acetyl-CoA. These results support a role for thiolase in the regulation of ketogenesis.

Acetyl-CoA C-Acetyltransferase↗
PubMed1976

Mitochondrial glycerol kinase activity in rat brain.

Glycerol kinase activity was found in the particulate fraction of rat brain homogenates predominantly associated with mitochondria. The enzyme remained bound to the particulate fraction after treatment with a variety of solubilizing agents.

Animals↗
PubMed1976

Growth of human diploid fibroblasts in the absence of glucose utilization.

Normal human diploid fibroblasts were able to undergo one to two cell divisions without glucose utilization in Eagle's minimum essential medium plus 10% dialyzed fetal calf serum if the medium was supplemented with hypoxanthine, thymidine, and uridine (supplemented medium termed HTU-MEM). Under these conditions, the added purine and pyrimidines were required for nucleic acid synthesis, as shown by the inability of Lesch-Nyhan fibroblasts to grow in HTU-MEM. Normal human diploid fibroblasts continued to produce lactate in HTU-MEM, but at a greatly reduced rate. Since cells grew in HTU-MEM without glucose utilization, the probable energy and carbon source was glutamine, which is present in relatively high concentration. Furthermore, the rate of glutamine utilization per cell division was 2-fold greater in HTU-MEM than in medium with 5.5 mM glucose. These results suggest that glutamine can be a major energy source for cells grown in vitro.

Cell Division↗
PubMed1976

Ability of exogenous alanine to lower blood beta-hydroxybutyrate during development in rats.

The intraperitoneal injection of L-alanine into 10- and 21-day-old fed Wistar rats resulted in blood alanine levels of 3-5 mM and in a rapid, significant decrease in the concentration of beta-hydroxybutyrate (betaOHB) in blood. The drop in betaOHB was unrelated to changes in the concentrations of pyruvate, lactate, or glucose. The intraperitoneal injection of glutamate at the same age had no effect on betaOHB values. In 2-day-old pups and in older weaned animals, the injection of alanine had either no effect or increased the levels of betaOHB in blood. The most rapid disappearance of exogenous alanine occurred in 35-day-old and not in 10- and 21-day-old rats. These data suggest that alanine has a depressant effect on the level of circulating betaOHB at a specific stage in the animal's maturation.

Alanine↗
PubMed1973

An alteration in glucose metabolism associated with a defect in ketone body metabolism.

Skin fibroblasts (CC-69) cultured from a patient with a unique syndrome of ketoacidosis associated with coenzyme A transferase (EC 2.8.3.5) deficiency showed an altered pattern of carbohydrate metabolism. These cells used glucose at a rate significantly less than controls (125 against 680 nmol/mg per hr). The oxidation of [6-(14)C]glucose to (14)CO(2) by these cells was also significantly diminished (12 against 350 pmol/mg per hr), but [2-(14)C]pyruvate and [1,4-(14)C]succinate oxidation by these cells did not differ from that by control cells. Measurements of glycolytic intermediates showed a reduction of several intermediates in the CC-69 cells that confirmed an inhibition of glycolysis between fructose-1,6-bisphosphate and pyruvate. The apparent inhibition in these cells could be reversed by an extended incubation of the cells in a buffered glucose solution. After 18 hr of incubation in 2.5 mM glucose, glucose uptake by the CC-69 cells increased 20-fold to 2560 nmol/mg per hr, whereas the rate for control cells remained constant at 640 +/- 90. Concomitant with this increase, [6-(14)C]glucose oxidation rose from 8 to 2261 pmol/mg per hr while controls remained constant at 428 +/- 175. This change was not due to new enzyme formation because incubation with puromycin had no effect on the increased use of glucose. Mixing experiments demonstrated no transfer of a permeable inhibitor or activating substances. In view of the deficiency of coenzyme A transferase in these cells, the data suggest an indirect regulatory role for this enzyme in peripheral tissue glycolysis.

Carbohydrate Metabolism, Inborn Errors↗