The metabolism of propionate in the isolated cow's udder

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Abstract
Excised cows'' udders were perfused with blood containing [1-C14]propionate, [1-Cl4]hexanoate or [3-C14]butyrate. In the [1-C14]propionate and [1-C14]hexanoate experiments, several acids of the Krebs cycle, pyruvate and gloxylate were isolated from the tissue. Glutamic acid was isolated from milk casein. In the [1-C14]butyrate experiment, succinic acid alone was isolated. The distributions of C14 in succinic acid and glutamic acid were determined by degradation. The C14 from [1-C14]propionate and [1-C14]-hexanoate was incorporated to a large extent into the acids of the Krebs cycle and to a smaller extent into pyruvic acid. The radioactivity of glyoxylic acid was very low in both cases. The C14 activity of succinic acid from the [1-C14] propionate and [1-C14]butyrate experiments was localized in the carboxyl groups. The C14 distribution in glutamic acid from the [1-C14]hexanoate experiment was different from that in glutamic acid from the [1-C14]propionate experiment. These results are consistent with propionate metabolism proceeding by the succinate pathway and there is no evidence for an alternate major pathway.