299 



Fialvio Perini 



pyridine nucleotide (PN)-oxidase, and to the photosynthetic 

 system. The latter may be the transhydrogenase described by 

 Lazzarini et al« '^^ 



FPNR 



This protein is obtained in oxidized form and has an absorp- 

 tion spectrum with broad maxima at k6^-k^0 and 14-00-420 mji. 



A ratio of 40 chlorophyll molecules to 1 atom of non haem iron 

 was determined from a chloroplast preparation ^•^^/. PPNR was 

 found only in photosynthetic forms of Euglena. 



ENZYMATIC ACTIVITIES 



The following enzymatic activities have been found in Euglena ; 

 l) succinnic dehydrogenase; 2) NADPH (reduced nicotinamide 

 adenine dinucleotide phosphate)- and NADH (reduced nicotinamide 

 adenine dinucleotide )-haemiprotein reductase (non-specific, 

 probably catalyzed by a transhydrogenase, NADPH is much better 

 coenzyme); 3) TPN-reductase (via ferrodoxin, i.e. PPNR, and 

 flavoprotein, may be the same as 2)); h) succinoxidase or PN-ox- 

 idase in presence of 95^ CO or C02/51^ O2. Reduced cytochromes 

 c-552 and 556 very poorly replace cytochrome c in a cytochrome 

 oxidase system. In the presence of cyanide (10 M) and low 

 oxygen tension, cytochrome 556 is oxidized more rapidly than 

 cytochrome a-605. On readmission of oxygen, cytochrome 55^ is 

 first reduced by the remaining substrate, and then oxidized, 

 whereas cytochrome a-605 exhibits a net oxidation which is more 

 rapid than under semi -anaerobic conditions. When oxygen becomes 

 available, cytochrome 556 is either not used, or participates in 

 processes before cytochrome a-605, in the respiratory system. 

 This investigation was made with fresh washed cells suspended in 

 biiffer, using the scattered transmission attachment of the Cary. 



The pathways, as shown on the next page, explain the resistance 

 of Euglena to some poisons and its resistance to anaerobic condi- 

 tions (11). In some cases the pathway going through a cytochrome 

 556-type may predominate, and a-type cytochromes may be present 

 in very small amounts, if at all. These mechanisms may explain 

 the unusual resistance to some metabolic poisons by many mlcro- 

 algae and protista, and the difficulty in finding any evidence 

 for a classical cytochrome oxidase. 



