Effect of yeast growth limitation on the respiratory chain, the economic coefficient and the critical oxygen concentration for respiration

The effect of the yeast growth limitation by oxygen on the economical coefficient (EC), the operation of the cyanide resistant electron transport pathway (CrETP), and the critical for respiration oxygen concentration concentration ([O2]cr) was studied. The operation of CrETP was found to differ among various yeasts growing on glucose: it could function during both the exponential phase and limitation of growth (Torulopsis candida), or only in the conditions of growth limitation (Candida tropicalis, C. mycoderma, C. lipolytica), sometimes for a very long period (Endomyces geotrichum); in certain cases (C. utilis), it cannot be detected at all. If the main respiratory chain is inhibited by cyanide (i. e. if only CrETP operates), the value of [O2]cr sharply increases; such an increase can be also found in the absence of cyanide but in the conditions of active operation of CrETP. Apparently, the value of [O2]cr is higher for cyanide resistant oxydase of the studied organisms than for cytochrome oxydase. A decrease in EC observed upon the limitation of yeast growth by oxygen (Lozinov et al., 1974) correlates with the appearance or intensification of CrETP. Therefore, the decrease of EC can be attributed to the operation of non-phosphorylating CrETP which occurs in all the studied yeasts (with an exception of C. utilis) when their growth is limited by oxygen.