Enzymes concerned in the synthesis of glycogen from glucose in the brown adipose tissue.

Under normal conditions glycogen cannot be detected in adipose tissue. When animals are first starved and then fed on a carbohydrate diet, glycogen appears temporarily in this tissue (see Hausberger & Neuenschwander-Lemmer, 1939). Tuerkischer & Wertheimer (1942) investigated the phenomenon in detail and found that, in the rat, this deposition of glycogen was particularly marked in the brown adipose tissue, which in this species is found between the scapulae as a light-brown butterfly-shaped mass, having the appearance of a gland. Glycogen concentrations as high as 6 g./100 g. wet tissue were sometimes observed. Fawcett (1948) has recently confirmed these observations. Mirski (1942) showed that brown adipose tissue of the rat contained phosphorylase and phosphoglucomutase and suggested that glycogen might be synthesized from glucose by a similar mechanism to that involving hexokinase and these enzymes in muscle and liver. Cori & Green (1943) and Cori & Cori (1945) showed that suitable preparations of muscle and spleen could convert crystalline muscle phosphorylase a into phosphorylase b, which was active only in the presence of adenylic acid. This effect of muscle and spleen was attributed to the presence of a 'PR' (prosthetic group-removing) enzyme, which was considered to remove a prosthetic group from phosphorylase a. Cori & Cori (1943) observed that the presence of extracts of liver or heart resulted in the synthesis by phosphorylase a from glucose-lphosphate of a polysaccharide similar to glycogen, while in the absence of such extracts there resulted a polysaccharide similar to amylose. They believed such extracts contained a 'Supplementary Enzyme' which, while phosphorylase a was forming, a-1:4glucoside linkages catalysed the introduction of branch points formed by a-1:6-glucoside linkages. The work described in this paper has demonstrated the presence of hexokinase in the brown adipose tissue of the rat, and has confinned the presence ofphosphorylaseandphosphoglucomutase ; the properties of the latter two enzymes have been investigated in more detail. Brown adipose-tissue extracts have also been found to possess PR enzyme and Supplementary Enzyme activities. EXPERIMENTAL