330 A. R. KRAIJ. 



f>;(Mi ill light. Of uiidci' carlx)!! monoxide^ in red liglit glA'es twice this 

 amount. liaising th(> infcnsily of llic while light under N2 gives .still 

 more of the maleiial. it", however, exposure to carbon monoxide con- 

 tinues for \/2 hour or more, tlie levels of 5a and 5b drop off sharply 

 with 5b dropping first, 'i'his decline occurs more quickly with carbon 

 monoxide than with nitrogen and occurs only under those conditions 

 which Avere found earlier (5) to ])iing about a drop in ability of the 

 tissue to fix carbon dioxide. It should be noted that exposure of the 

 tissue to carbon monoxide in yellow light affects the tissue no differ- 

 ently from exposure to white light in air. 



The presence of these materials is not completely dependent on 

 light, e.g., low levels of 5b are observed under dark aerobic con- 

 ditions and low levels of 5a under dark anaerobiosis. It is not yet 

 certain whether 5a and 5b depend on carbon dioxide uptake for their 

 maintenance. It is probable that they do not since they take up C^^ 

 very slowly and only under conditions of net growth. Also the level of 

 neither compound drops rapidly when placed under C02-free nitrogen 

 in light, whereas those of photosynthetic products, e.g., sugar phos- 

 phates, show a fairly rapid decline. 



These data indicate that 5a is convertible to 5b by a dark reaction. 

 Since the 5a piles up under anaerobic conditions, the reaction must be 

 oxidative and 5a more reduced than 5b. The close parallel between 

 the level of 5a and intensity of illumination indicates a close relation 

 between formation of 5a and light. The short time required to produce 

 high levels — less than 50 milliseconds — indicates an extremely close, 

 perhaps direct, relation. The comparatively rapid loss of both 5a and 

 5b on cessation of oxidation indicates that some product of oxidation, 

 probably high-energy phosphate bonds, is necessary for their main- 

 tenance. Nothing has yet been observed which would be incompatible 

 with the hypothesis that 5a is an acceptor in the photolysis of water 

 and is converted to 5b by an oxidative, CO-inhibited process. 



What, chemically, are these compounds? It is possible to label them 

 with P*2^ Qi4^ g^j-,(;j g35 'pjjg process of labeling is slow with P*- and still 

 slower with S^^ and C'^. The last two are incorporated into 5a and 5b 

 in Chlorella only in growing cell suspensions. Thus the compound in 

 vivo is a relatively stable one as far as C^^ and S^^ are concerned. 

 Chromatographic and spectrophotometric analysis of 5a and 5b 

 have shown that they are not pyridine nucleotides, flavins, menadione, 

 or ascorbic acid. The 5b area contains more than one compound: the 



