Abstract
It was previously reported that sodium monoiodoacetate (hereinafter called IA) inhibits lactic production in Streptobacterium casei as it does in higher forms. 1 This organism is especially advantageous for a comparative study of lactic acid fermentation, since a single compound, e. g., glucose, will suffice as a source of energy. The glucose supplied is quantitatively converted to lactic acid, and in the absence of nitrogenous compounds—essential for growth—there seems to be no other significant metabolism. 2 Furthermore there is evidence that the course of lactic acid formation by Streptobacterium casei is qualitatively the same as in other forms. 3
The production of lactic acid is a reaction of great importance and of widespread occurrence, being the physiological equivalent of respiration in some forms and its supplement in others. 4 Like oxidation it involves a chain of reactions which are primarily dehydrogenations. The results of our experiments serve to elucidate further some of the properties of the enzymes concerned in lactate fermentation and to indicate still another analogy with biological oxidation.
Lactic acid production was determined by the method of Warburg. 5 The reaction vessels were filled with a gas mixture consisting of 5% carbon dioxide and 95% nitrogen. The required amounts of IA were placed in the sidearms of the vessels and added after a preliminary control period. In the several controls, which received no IA, after a brief induction period the rate of lactic acid formation remained constant for more than 7 hours. In all cases the organisms were suspended in a solution of 2.0% glucose and 0.5% sodium bicarbonate. Little change in pH occurred during an experiment, the lowest final value noted being pH 6.7.
When IA is added to such a system there is a definite “latent period”, which is doubtless a function of cell membrane permeability and diffusion rate of IA.
Get full access to this article
View all access options for this article.