The use of paper chromatography for in vivo studies of lactose metabolism in mammary-gland preparations

Abstract

Various preparations from lactating mammary glands of guinea pigs and rats were used to study the metabolism of lactose in vitro. The formation of lactose and the fate of substrates added to the preparations were followed by paper chromatography. A chromatographic method was developed by which rates of synthesis of lactose could be measured after incubation of tissue slices in Warburg manometer vessels. Lactose was not broken down by respiring tissue slices, blends or mitochondrial suspensions, but crude aqueous extracts showed some lactase activity, particularly when the pH was lowered. The synthesis of lactose obtained by Grant (1935) in surviving mammary tissue slices from guinea pigs was confirmed, but no synthesis was obtained with rat tissue. The synthesis was supported by glucose and showed a greater proportional increase with glucose concentration than did glucose oxidation. It was not increased by the partial replacement of glucose by other substrates. The synthesis was dependent on aerobic conditions and was inhibited by 0.2 m[image] dinitrophenol. No synthesis of lactose was gained with blends or with mitochondrial suspensions prepared from guinea-pig tissue. Succinate and alpha-oxoglutarate were apparently not oxidized beyond fumarate by mitochondrial suspensions from guinea-pig mammary gland.