THE INCORPORATION OF CARBON DIOXIDE INTO MILK CITRATE IN THE ISOLATED PERFUSED GOAT UDDER

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Abstract
Isolated perfused goat udders supplied with glucose, acetate and amino acids were infused for several hours with NaHC1403. Lactose, milk-fat fatty acids and glycerol had very little radioactivity. The specific radioactivity (counts/min./mg. of C) of milk citrate was 9-16% that of the carbon dioxide in the perfusion fluid and 19% that estimated for tissue carbon dioxide. The specific radioactivity of tissue citrate resembled that of milk citrate. The radioactivity in citrate was predominantly in C-6, suggesting some carboxylation of [alpha]-oxoglutarate in addition to carboxylation of C3 compounds. [l-C14]Glutamate was infused in a similar experiment, and milk citrate radioactivity was predominantly in C-1+C-5. The results are discussed in relation to the contribution of glucose and acetate carbon to citrate. The implications of the carboxylation of [alpha]-oxoglutarate are considered.