Carbohydrate metabolism in blood cells studied by means of isotopic carbon
The breakdown of 14 C-labelled glucose, pyruvate and lactate to yield radioactive carbon dioxide has been studied in the blood of cats, rabbits and dogs incubated outside the body at 37°C. The process has been shown to be dependent upon access to oxygen and to be greatly depressed by cooling the incubation mixture to 0°C, or by previous beating of the blood to 100° C. The enzymic nature of the reactions involved is further indicated by the effects of a number of know n enzyme poisons. Fractionation of rabbit blood has demonstrated that the active elements in the production of radioactive carbon dioxide are the white cells, and it has been calculated that the rate of their oxidative metabolism can account for the complete breakdown of 0*3 mg glucose per 100 ml. of blood per hour. The finding that arsenite strongly inhibits the oxidation of pyruvate without greatly affecting that of glucose points to the operation of a direct oxidative pathway for glucose not involving the usual glycolytic series of intermediates, that is, the so-called ‘hexose-monophosphate shun t5. The idea that such a mechanism functions in the leucocytes is supported by the results of experiments with inhibitors other than arsenite, and by the observation that glucose labelled only in the 1-carbon atom is a richer source of radioactive carbon dioxide than uniformly labelled glucose of the same specific activity.