Past work in this laboratory has shown that the stationary populations of 8. cerevisiae produced in a yeast extract medium during serial transfer under continuous anaerobic conditions mere quite small, while excellent growth occurred in the presence of oxygen (Brockmann and Stier, '47). It was also shomm that the anaerobic population could be greatly increased by supplementing the medium with various crude materials, such as vegetable oils, malt sprouts and distillers' dried solubles, or their unsaponifiable fractions. This Pesult indicated that sterols might have special significance in the anaerobic growth of yeast (Stier and Scalf, '49; Stier et al., '50; Scalf and Stier, '50).In order to proceed with studies on the role of sterols in anaerobic growth, it was necessary to change from the yeast extract medium that had been used in previous work to a chemically defined basal medium. It is the object of this report to describe this medium and especially to show the effect on anaerobic growth of adding a yeast sterol, ergosterol, to this medium. A comparison of anaerobic and aerobic growth is also given. EXPERIMENTAL PROCEDURESYeast strnirz. All experiments were conducted with a distillery type yeast; a strain of S. cereuisiae, SC-1 (DCL),

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IWe will discuss in this paper the kinetics of endogenous respiration of bakers' yeast; that is, the respiration of intact yeast cells suspended in non-nutrient media. In succeeding papers results growing from an examination of the nature of the metabolic processes involved will be presented. The purpose of this series is to demonstrate the necessity of describing the behavior of metabolic systems at their native loci by the use of in vivo procedures. By dealing with experimentally verifiable rate-controlling steps in the various metabolic systems we will show how these complex chains of reactions may behave as distinct functional units at one time and, depending upon the imposed experimental conditions, as interrelated but yet coordinated systems. Since the overall metabolic activity can be shown to be governed by these rate-controlling "loci, ''1 integrated action of the myriads of simultaneous reactions is achieved within a cell. It is felt that this method of investigation is a necessary procedure which should precede any final application of the results of in vitro studies of enzyme action to the dynamical organization of in vivo metabolic processes.As a general rule in plant cells and tissues the rate of respiration under starvation conditions sooner or later decreases with time after the stored material has been reduced below a certain "critical concentra-1 Obviously in all but "zero order reactions" (for an example, cf. p. 471) the instantaneous rate of respiration may be a function of the concentration of reacting materials. The rate constant in these cases is then the appropriate constant describing the activity of the pace-setting locus; e.g., a first order constant. We imply that the behavior of the descriptive constant for the rate of decomposition of a relatively large amount of substrate reflects the physical and chemical characteristics of this locus, whatever its real nature may be.

IIn a previous paper concerned with a kinetic analysis of endogenous respiration of bakers' yeast (Stier and Stannard, 1935-36) it was shown that the rate of respiration was a function of the time in the "non-nutrient" medium, the age of the cells, and their previous history. The rates of both O, consumption and CO, production were equal under almost all conditions. Evidence was summarized to show that the dissimilated substrate is a carbohydrate, probably glycogen. The statement was made that the term endogenous respiration is preferable to "autofermentation" in referring to the metabolic utilization of stored glycogen in intact bakers' yeast cells. This change in terminology was based mainly upon the results of investigations reported in the present paper.It is usually assumed that the decomposition of stored glycogen proceeds within the yeast cell by the same mechanisms as the respiration and fermentation of simple carbohydrates placed in the external medium.l We will show in this account that dissimilation of the available carbohydrate reserves proceeds by way of a "unit" chain of reactions resulting in a complete oxidation of the carbohydrate to CO, and I-I,O. Since "pure" respiration only is involved we may speak of "the respiratory character of endogenous metabolism" or may refer directly to the process as "endogenous respiration." We will also show that the endogenous chain of reactions behaves as a distinct functional unit only when the structural integrity of the cell is maintained. Its unitary character is thus the property of a "chambered architecture" of the yeast cell (cf. Hofmeister, 1901).1 By fermentation we mean anaerobic CO, production and the accumulation of alcohol in the medium.