BARBARA PET RACK AND FRITZ lAPMANN 623 



variety of substances, however, it iiUerlcrecl with stiuUes on the effect 

 of some inhibitors upon photophosphorylation. 



Sacktor, O'Neill, and Cochran (12) reported that the activation of 

 (light nniscle mitochondria by BSA appeared to depend on the pres- 

 ence of sulfhydryl (SH) groups on the protein. Since Vennesland's 

 group (8) described a variable stimulation of photophosphorylation 

 by glutathione (GSH), we examined the relationship between the 

 effect of BSA and GSH on photophosphorylation. Table 1 illus- 

 trates the seemingly unpredictable fluctuations of such effects. This 

 variation does not seem to be due to preparative procedures but ap- 

 pears to reflect differences in the algal cells from batch to batch. 

 Similar variable effects of GSH have been observed with microsomes, 

 Avhere activity lost on ageing was found to be restored by GSH (6) . 



In experiment 1 of Table 1, high rates are observed in the absence 

 of both BSA and GSH, and no further increase is found in their 

 presence. In experiment 2, the observed rate in the absence of both 

 is low, but either GSH or BSA will stimulate, and the effects are not 

 additive. This would suggest that it is the SH groups on BSA that 

 produce the activation. In experiment 3, however, GSH is unable to 

 replace BSA as activator; but most of our preparations were activated 

 by either compound. 



Under optimum conditions, Anahaena fragments photophosphory- 

 late at a rate of 200-400 ^moles inorganic phosphate (Pj) consumed 

 per hour per mg chlorophyll at 30 °C in Ng. Rates are proportional 

 to chlorophyll concentration up to 0.3 mg in 3 ml, and remain con- 

 stant up to 30 minutes. More active preparations are obtained from 

 48-hour cultures than from cells grown to maximum density. The 



TABLE 1 

 Effect of GSH and BSA on Photophosphorylation 



Experiment - GSH + GSH - GSH + GSH 



- BSA - BSA + BSA + BSA 



^moles APi/hr/mg chlorophyll 



1 404 488 488 512 



2 58 215 223 217 



3 165 199 



Reaction media. Each tube contained the following in Mmoles/2.7 ml: 20 potassium 

 phosphate pH 1.1, 200 Tris buffer pU 1.1, 25 glucose, 2 ADP, 20 MgCl., 0.4 PMS, 

 excess hexokinase, Anabaena fragments containing approximately 0.15 mg chlorophyll, 

 and where shown, 1 jumole GSH and 6 mg BSA. The incubation was for 15 minutes 

 at 30°C in light and nitrogen. The reaction was stopped with 0.3 ml 509c TCA. 

 P, was measured according to Fiske and Subbarow. 



