fide formation with protein mercaptan groups is not responsible for the change in absorption spectrum is indicated by the failure of the mercaptans MEA and MEG to cause a similar change.
However, it is again possible that salt formation has taken place with catalase since the over-all shape of the sum of the absorption curves has not been appreciably altered in the mixture, and the average difference in absorbance, 0.040, is not greatly different from those of the previous cases where salt formation is suspected. Moreover, it appears that complex formation of enzymes may be demonstrated by this method of absorbance differences in absorption spectra in certain cases at least.
Conclusions
Spectrophotometric evidence has been found that a known antiradiation agent, sodium diethyldithiocarbamate, undergoes complex formation with lactic dehydrogenase and either salt or weak field complex formation with catalase. No definite evidence for complex formation of these enzymes with either 2-mercaptoethylamine or 2-mercaptoethylguanidine was found, although salt or weak field complex formation is possible. Apparently, any complexation by the latter agents is more readily dissociable than that by the dithiocarbamate.
No spectrophotometric evidence of complex formation between salicylate and either lactic dehydrogenase or catalase was found, although both enzymes are known to be inhibited by salicylate. It is possible that any complex formed has dissociated too rapidly to be observed by this method.