On the Cytochromes of Anaerobically Cultured Yeast 231 



with a large quantity of small particles organized in clusters. Fraction II 

 contains small particles organized in clusters and no mitochondria. Fraction 

 III (very scanty), contains free granules of homogeneous size only and no 

 mitochondria. These three fractions have the same haematin spectrum 

 (Fig. 5) but that of fraction II is by far the stronger. The spectrum of these 

 fractions contains bands situated at 552-5 (a), 525 (/?); and 558 (a), 532-5 (/?) 

 m/<, reducible by dithionite only; the first two bands are sharper than 

 the second two. We have established that these components cannot be 

 reduced by reduced diphosphopyridine nucleotide (DPNH) or by lactate; 

 cytochrome b^ (lactate dehydrogenase) thus does not correspond to these 

 haematin compounds (Bach, Dixon and Keilin, 1942; Appleby and Morton, 

 1954, 1959; Boeri and Tosi, 1956). 



DISCUSSION AND CONCLUSIONS 



1. Our spectrographic studies at low temperature of yeast cells cultured 

 anaerobically have shown that the haematin spectrum in the exponential 

 phase of growth, when reduction is brought about by endogenous substrates, 

 includes three a-bands located at 552-5, 558 and 575 mix (Chaix and 

 Heyman-Blanchet, 1957). Lindenmayer and Estabrook (1958) have confirmed 

 the presence of a-bands at 552-5 and 558 m/< (to be precise these authors 

 found the bands at 551 and 557-5 m/{) but they did not find the a-band at 

 575 m//, no doubt because their preparations were reduced by dithionite and 

 not simply by the endogenous substrates. In fact, this band at 575 mfi, 

 which probably belongs to an oxyhaemoglobin (Keilin, 1953; Keilin and 

 Tissieres, 1954) disappears in the presence of dithionite. 



During the stationary phase of anaerobic growth, the absorption bands of 

 the exponential phase tend to weaken and three new bands appear, situated 

 at 540 m/i and 585 mfx (Lindenmayer and Smith, 1957) and 630 m/< of which 

 the physiological significance remains obscure. 



2. During the induction by oxygen of the respiratory system of cells 

 harvested in the exponential phase of anaerobic growth the two bands at 

 552-5 and 558 m/( never disappear. The col and {a + a^ a-bands simply 

 appear little by little, just as though the ba. and c^a bands of the classical 

 spectrum correspond to the bands at 552-5 and 558 m/^t which exist before 

 the intervention of oxygen, or are superposed on these. On this point our 

 observations do not agree with those of Lindenmayer and Estabrook (1958), 

 who considered that passage from anaerobiosis to aerobiosis entailed only 

 displacement of the 557-5 band to 559 m/f and of the 551 band to 548 m^, 

 the qa band at 554 m/« appearing secondarily only. 



As regards the kinetics of the induction by oxygen with cells in the exponen- 

 tial phase on the one hand and in the stationary phase on the other, our 

 findings are the same as those of Slonimski (1956) and Lindenmayer and 

 Estabrook (1958). The speed of induction is much greater in the second case 



