372 



R. W. Henderson and W. A. Rawlinson 



column (Armstrong, Coates and Morton, 1958, and this volume, p. 385). The 

 value of +0-28 V with « = 1 at pH 6-4 and 25°C was obtained (Fig. 1 ; see 

 also Henderson and Rawlinson, 1958). 



20 40 60 80 100 



Reduction, % 



Fig. 1. Oxidation-reduction titration at pH 6-4 of yeast cytochrome c. 

 Solid line is theoretical curve for Eq = 0-282 V, « = 1. 



COMBINATION OF CYTOCHROME C FRACTIONS 

 WITH COPPER 



Inhibition of Copper-catalysed Oxidation of Ascorbic Acid 



One of the most striking effects of proteolytic digestion of M. heart c is 

 the induction of a high ascorbic acid oxidase activity which parallels a loss 

 in activity in the usual biological oxidase systems (Tsou, 1951b). Margoliash 

 (1954b) observed a similar effect with a fraction separated on a resin column. 



When examining the ascorbic acid oxidase activity of a number of M. 

 heart c fractions we observed that in the case of the '0-34% Fe' or 'low-iron' 

 content samples, lower oxygen-uptake values were obtained than for the 

 ascorbatc blank. A similar reduction in oxygen-uptake of the blank was 

 obtained by addition of ethylenediaminetetraacetic acid (EDTA) (Fig. 2). 



