| Abstract: | A comparative study of the pyruvate dehydrogenase complex and its pyruvate dehydrogenase component was carried out by using the circular dichroism method. It was found that the spectral properties of the pyruvate dehydrogenase complex are determined by those of its first component: i) the spectrum of the thiamine pyrophosphate-free pyruvate dehydrogenase complex displayed the main characteristics of the pyruvate dehydrogenase component; ii) the appearance of the charge transfer complex band during thiamine pyrophosphate saturation was revealed for the both proteins; iii) in both cases the charge transfer complex band disappeared after the interaction of the holoform with pyruvate and reappeared after the addition of dithiothreitol used as a deacetylating reagent. Coenzyme A in the same reaction selectively deacetylated the pyruvate dehydrogenase complex (but not its pyruvate dehydrogenase component). The spectral dynamics of pyruvate dehydrogenase reflects the functional changes in the enzyme active centers during the catalytic act. The similarity of the spectral behaviour of pyruvate dehydrogenase within the complex structure and in the isolated state provides support for the earlier proposed mechanism of the pyruvate dehydrogenase action and ensures a methodological basis for its direct investigation within the complex structure. |
