Pyruvate radioactively labeled at its carboxyl carbon enters aerobic respiration in yeast cells. Where does the label appear next?

Core Concept

The pyruvate dehydrogenase complex catalyzes oxidative decarboxylation: the carboxyl carbon of pyruvate splits off as CO2 while the remaining two carbon acetyl unit transfers to coenzyme A. Labeling studies confirm this carbon exits immediately as CO2, contributing nothing to citrate or other cycle intermediates. Each subsequent turn of the cycle then liberates two further CO2 molecules derived from acetyl positions.