Abstract This paper deals with the partial purification of the pyruvate dehydrogenase complex (PDC) from chloroplasts of spinach and maize mesophyll which hitherto has been isolated only from pea chloroplasts. Starting with membrane free suspensions of lyophilized chloroplasts, and following a high-speed (140000 Xg) centrifugation of this “stromal extract”, the initial specific PDC-activities were concentrated by a factor 10 in the sediment. While most of the purification procedures described earlier resulted in almost complete loss of enzyme activities, a rate zonal sedimentation on linear glycerol gradients allowed for an additional up to 100-fold enrichment of the labile multienzyme complex, albeit with low yields. In contrast to chloroplast PDC from maize mesophyll, inactivation of the spinach complex during glycerol fractionation was due to the dissociation of its loosely bound dihydrolipoyl dehydrogenase component which collected in a lower density fraction of the gradient. Its recombination with PDC constituents of the bottom layer nearly restored initial activities. The chloroplast complex has been identified as true PDC by its substrate specificity for pyruvate, NAD+, and coenzyme A and the 1:1:1 stoichiometry of its reaction products NADH, CO2, and acetyl-CoA. The chloroplast PDC of both plant species showed the well known higher pH-and Mg-requirements than the mitochondrial complex. The observed species-specific differences in the stability of this multienzyme system suggest a connection with the aggregation state of its components. Apparently, the individual subcomplexes are able to function either together in acetyl-CoA formation or independently from each other, e.g. in the synthesis of acetolactate via hydroxy-ethyl-thiamine pyrophosphate or dihydrolipoyl dehydrogenase activities.
Identification of a Novel Dihydrolipoyl Dehydrogenase-binding Protein in the Pyruvate Dehydrogenase Complex of the Anaerobic Parasitic Nematode,Ascaris suum
