The Metabolism of [ 1 - _ 4 C ] Glucose in an Enzyme System from Propionibacterium

Wood, Stjernholn & Leaver (1955) have proposed that propionic acid fermentation may involve the simultaneous occurrence of the Embden-Meyerhof cleavage and a second, undetermined, cleavage. The suggestion was based on the distribution of 14C in the products obtained by fermenting [1-14C]glucose, [2-l"C]glucose, [6-14C]glucose and [3:4-14C]glucose with cell suspensions. No matter which carbon atom of the glucose was labelled, there was considerable radioactivity in all the carbon atoms of the products. Although the widespread distribution of 14C can probably be accounted for by the Embden-Meyerhof cleavage and subsequent randomization of 14C via symmetrical C4-dicarboxylic acids, and possibly via a symmetrical C3 intermediate, the occurrence of a pathway other than the Embden-Meyerhof cleavage in whole cells is indicated by the following considerations: (1) The carbon dioxide formed from [1-14C]glucose had a higher activity than any of the carboxyl groups of the end products and a much greater activity than the carbon dioxide from [6-14C]glucose; (2) the acetate from [1-14C]glucose had a higher activity than that from [6-14C]glucose; (3) the peculiar distribution of 14C in the products from the other types of labelled glucose suggested the existence of an unknown metabolic pathway. In order to obtain more detailed information about the mechanism it appeared desirable to have a cell-free enzyme preparation which could carry out the whole or part of the propionic acid fermentation. It has been found that such an enzyme system can be obtained by sonic disintegration of propionic acid bacteria. The preparations form propionate, succinate, acetate and carbon dioxide from [1-14C]glucose and the 14C is randomized into all positions of the products. The enzyme system of Propionibacterium 8hermanii is remarkable in that it promotes a net uptake of carbon dioxide when glucose is metabolized.