Acetone Metabolism 229 



The results with dififerent types of labelled fatty acids are 

 also in accord with the predictions of j8-oxidation and thus 

 lend support to the occurrence of these reactions in the intact 

 animal (Lifson, Lorber, Sakami and Wood, 1948). 



The recent investigations by Sakami best illustrate the 

 usefulness of glycogen as an indicator of metabolism. His 

 first studies on formate metabolism (Sakami, 1948) were 

 based on this technique and led to the discovery that formate 

 is incorporated in the j8-carbon of serine. It was known that 

 glycine was glycogenic but there was no known mechanism 

 for a net synthesis of glycogen from glycine. The most 

 attractive explanation appeared to be the one shown below 

 which included reversal of the reaction which Shemin (1946) 

 had postulated for the formation of glycine from serine. 



IP^COOH+CHsNHgi^COOH -> i^CHgOH • CHNHg • i=^COOH 

 i^CHsOH • CHNH2 • 13C00H -> 14CH3 • CO • i^COOH 

 214CH3 • CO • 13C00H -> 14C . 14C . i4,i3C . 14,13C . 14C . 14C 



^*C-Formate and CHgNHa^^COGH wxre therefore given to 

 rats and the glycogen w^hich was formed w^as isolated and 

 degraded. The ^^C was found only in the 3, 4 carbons and 

 the highest ^*C labelling was in the 1, 6 carbons. These 

 results, therefore, fit the predicted distribution pattern of the 

 glycogen as made from the above equations. To verify further 

 the scheme, Sakami (1948) isolated serine from the liver pro- 

 tein of the above experiments and degraded it by periodic 

 acid oxidation to obtain formaldehyde (/8-C), formate (a-C) 

 and CO 2 (carboxyl-C). The labelling of the serine was found 

 to agree with the above equations, i.e. the ^*C was in the 



in the 3, 4 positions so even a small fixation in other positions should have 

 been detectable. 



Another interesting example of a new type of fermentation is that studied 

 by Lampen, Gest and Sowden (1951). [l-^^CJ-Xylose was fermented with 

 Lactobacillus pentosus and gave the following labelling of products: — 



"C-C-C-C-C-^^CHj • COOH + COOH CHOH CH3 

 12 3 4 5 



The aldehyde of the xylose thus becomes the methyl group of acetate. 

 What part the reversal of such a cleavage may play in the synthesis of pentose 

 is a question of great interest. 



