An acute intraperitoneal injection of ethanol (0.7 or 2.1g/kg body wt.) causes the reversible, dose-dependent accumulation of hepatic triglyceride in rats. By using a pulse of [14C]palmitate injected into a tail vein, it was found that ethanol (2.1g/kg)had no effect on the flux of unesterified fatty acid of serum (4.3mumol/min per 100g body wt.). However, either dose increased the fraction of the total flux going to liver from 0.16 to0.27 as rapidly as could be measured (30s), and it remained elevated until all ethanol had been cleared from the blood. The fraction of the total radioactivity in lipids of liver that was in triglyceride increased linearly for 1 h from 30 to 50% and there was a simultaneous decrease in phospholipid from 60 to 40%. The rate of synthesis of hepatic triglyceride derived directly from unesterified fatty acid of serum was calculated by using the flux rate of unesterified fatty acid in serum, the fractional hepatic uptake of this flux, and the percentage of liver fatty acid esterified to triglyceride. This contribution is related to the total synthetic rate of hepatic triglyceride (rate of accumulation+rate of release) to determine quantitatively how much of the developing fatty liver is attributable to increased uptake of unesterfied fatty acid of serum. At the higher dose of ethanol, about half of the accumulating triglyceride is derived from this source, whereas with the lower dose of ethanol it can account for all of the build-up.

Objective: FLASH irradiation reportedly produces less normal tissue toxicity, while maintaining tumour response. To investigate oxygen’s role in the ‘FLASH effect’, we assessed DNA damage levels following irradiation at different oxygen tensions, doses and dose rates. Methods: Samples of whole blood were irradiated (20 Gy) at various oxygen tensions (0.25–21%) with 6 MeV electrons at dose rates of either 2 kGy/s (FLASH) or 0.1 Gy/s (CONV), and subsequently with various doses (0–40 Gy) and intermediate dose rates (0.3–1000 Gy/s). DNA damage of peripheral blood lymphocytes (PBL) were assessed by the alkaline comet assay. Results: Following 20 Gy irradiation, lower levels of DNA damage were induced for FLASH, the difference being significant at 0.25% (p < 0.05) and 0.5% O2 (p < 0.01). The differential in DNA damage at 0.5% O2 was found to increase with total dose and dose rate, becoming significant for doses ≥20 Gy and dose rates ≥30 Gy/s. Conclusion: This study shows, using the alkaline comet assay, that lower levels of DNA damage are induced following FLASH irradiation, an effect that is modulated by the oxygen tension, and increases with the total dose and dose rate of irradiation, indicating that an oxygen related mechanism, e.g. transient radiation-induced oxygen depletion, may contribute to the tissue sparing effect of FLASH irradiation. Advances in knowledge: This paper is first to directly show that FLASH-induced DNA damage is modulated by oxygen tension, total dose and dose rate, with FLASH inducing significantly lower levels of DNA damage for doses ≥20 Gy and dose rates ≥30 Gy/s, at 0.5% O2.

No abstract

No abstract

No abstract

No abstract

Oxidative phosphorylation is a vital process in the economy of aerobic cells, probably accounting for over 90 percent of all the adenosine triphosphate (ATP) generated from adenosine diphosphate (ADP) and phosphate at the expense of the energy liberated during catabolism of foodstuffs. Despite the great importance of this process and 20 years of intensive investigation, the enzymatic-details of oxidative phosphorylation are still essentially unknown. It is certain, however, that during the exergonic passage of a pair of electrons from substrate to molecular oxygen, via the pyridine nucleotides, flavoprotein, and the cytochromes, 3 moles of ATP are generated in coupled reactions occurring at three points in the respiratory chain (1-3), presumably those shown in the upper portion of Fig. 1.Both electron transport and oxidative phosphorylation take place in mitochondria, the structure of which must be relatively intact in order that oxidative phosphorylation may be observed in vitro. This finding has greatly limited the experimental approaches to the enzymatic mechanisms involved; it is largely for this reason that the mechanism of oxidative phosphorylation remains one of the most conspicuous mysteries in contemporary biochemistry.In the last three years we have studied experimental procedures for making morphologically less organized preparations from rat liver mitochondria with which the enzymatic details of oxidative phosphorylation could be more directly studied, with the ultimate goal of resolving the mechanism of oxidative phosphorylation by enzyme separation and reconstruction approaches. We have found it possible to obtain fragments of the mitochondrial membrane which contain relatively intact respiratory chain assemblies, including the enzymes neces-450 sary for coupling phosphorylation to electron transport. This article summarizes the chemical and enzymatic properties of these membrane fragments, prepared by the action of digitonin on rat liver mitochondria, and the new information they have yielded concerning the mechanism of oxidative phosphorylation and its relation to other aspects of mitochondrial physiology. *Membrane FragmentsPreparation. Washed rat liver mitochondria are suspended in 0.05M sucrose and treated in the cold with an 0.8-percent solution of recrystallized, metal-free digitonin. The mitochondria undergo virtual dissolution, leaving a turbid brown solution which is centrifuged at 50,000 g for 25 minutes. The supernatant fluid, which is not clear but contains a gelatinous material, is then centrifuged at 100,000 g for 25 minutes to sediment the phosphorylating membrane fragments (4, 5). When suspensions of this preparation are incubated aerobically with D-(3-hydroxybutyrate, ADP, and orthophosphate, oxygen is taken up, acetoacetate accumulates in equivalent amounts, and inorganic prosphate (Pi) disappears with equivalent formation of ATP. The observed P:2e ratios (moles of Pi taken up per pair of electrons transferred) have been as high as 2.8 [maximum expected, 3.0 (2)] but are more usua...

No abstract