STUDY OF BIOLOGICAL SIGNIFICANCE OF CYTOCHROME METHYLATION .1. THERMAL, ACID AND GUANIDINIUM HYDROCHLORIDE DENATURATIONS OF BAKERS-YEAST FERRICYTOCHROMES C

The iso-cytochromes c from baker''s yeast: iso-1 methylated and unmethylated forms and iso-2 were purified and their stabilities towards denaturants compared to that of horse heart cytochrome c. Thermal, acid and guanidinium hydrochloride denaturations were followed using fluorescence emission of their trp 59 and/or the absorbance in the Soret region as the physical parameters. Very few differences could be evidenced among the ferricytochromes investigated in this study insofar as the acid denaturations are concerned. Thermal and guanidinium hydrochloride denaturations studies clearly showed the ferricytochrome from horse heart to be much more stable than those from baker''s yeast. No appreciable differences could be measured among the methylated and unmethylated forms of iso-1 cytochrome c nor among iso-1 and iso-2 cytochromes from baker''s yeast. A stabilizing effect of methylation on the tridimensional structure of ferricytochrome c must probably be discarded. Other possible physiological roles of methylation are suggested taking into account the relative instability of ascomycete''s cytochromes as compared to mammalian ones.