Some Photochemical Experiments with Pure Chlorophyll. 35T 



activity of the enzyme being affected by the different experimental conditions 

 in the various tubes. Sorensen (9), however, has emphasised the fact that for 

 many enzyme actions there is not only a temperature optimum but also a 

 definite concentration of hydrogen ions at which maximum activity is 

 obtained. For catalase Sorensen found that the optimum activity was 

 obtained at absolute neutrality, diminishing with increase both of acidity and 

 of alkalinity. In Usher and Priestley's experiments the catalase was mixed 

 with gelatine, into which carbon dioxide would diffuse, and the increased 

 acidity resulting would inhibit the action of the catalase. 



The result of Usher and Priestley's experiments would then be explained 

 thus : 



1. The production of formaldehyde is always due to the oxidation of 

 chlorophyll or the accompanying substances in the crude chlorophyll. 



2. The bleaching is due to the oxidation of chlorophyll under the action of 

 light. 



3. The inhibition of bleaching in the tube 1 in the experiment referred to 

 above is due to the catalase system preventing the oxygen from acting on 

 the chlorophyll. 



4. The formaldehyde production in tube 4 is due to the decrease in the 

 activity of the catalase system owing to the acidity produced by carbon 

 dioxide, formaldehyde being produced by oxidation of the chlorophyll. 

 Unfortunately tube 2 was not examined for formaldehyde. 



b. Theory of Wager. 



Wager (11) observed an active absorption of oxygen by his chlorophyll 

 extract and the formation, as the result of oxidation, of considerable 

 quantities of formaldehyde. On these two observations Wager suggests a 

 theory of carbon assimilation in which carbon dioxide is in one way or 

 another " built up independently into the chlorophyll molecule," and the 

 carbohydrate production then " initiated by the photo-oxidation of chloro- 

 phyll and subsequent polymerisation of the aldehyde thus formed, rather 

 than by the direct photo-synthesis of carbon dioxide and water." 



Neither of the two observations on which the theory is based can be 

 considered satisfactory. It has been shown by Willstatter that it is only the 

 yellow pigments which are able to absorb oxygen with rapidity and in large 

 quantities. As Wager states that he worked with a crude alcoholic extract 

 of the leaf pigments, evaporated to dryness and redissolved in petrol-ether, 

 the rapid absorption of oxygen observed by him must almost certainly have 

 been due to the yellow pigments, and cannot therefore be used in support of 

 a theory of the action of chlorophyll. 



