THECOMPLEXFATE OFα-KETOACIDS

Abstract

Plant cells are unique in that they contain four species of alpha-ketoacid dehydrogenase complex: plastidial pyruvate dehydrogenase, mitochondrial pyruvate dehydrogenase, alpha-ketoglutarate (2-oxoglutarate) dehydrogenase, and branched-chain alpha-ketoacid dehydrogenase. All complexes include multiple copies of three components: an alpha-ketoacid dehydrogenase/decarboxylase, a dihydrolipoyl acyltransferase, and a dihydrolipoyl dehydrogenase. The mitochondrial pyruvate dehydrogenase complex additionally includes intrinsic regulatory protein-kinase and -phosphatase enzymes. The acyltransferases form the intricate geometric core structures of the complexes. Substrate channeling plus active-site coupling combine to greatly enhance the catalytic efficiency of these complexes. These alpha-ketoacid dehydrogenase complexes occupy key positions in intermediary metabolism, and a basic understanding of their properties is critical to genetic and metabolic engineering. The current status of knowledge of the biochemical, regulatory, structural, genomic, and evolutionary aspects of these fascinating multienzyme complexes are reviewed.

Mitochondrial Protein Lipoylation Does Not Exclusively Depend on the mtKAS Pathway of de Novo Fatty Acid Synthesis in Arabidopsis

“…First, we have recently shown that a total knockout of GDC is lethal even in nonphotorespiratory conditions, indicating that GDC fulfils a nonreplaceable function in vital metabolic processes other than photorespiration (Engel et al, 2007). Second, in addition to H protein, other mitochondrial proteins of strategic importance, mainly the E2 subunits of the a-ketoacid dehydrogenase complexes PDH and KGDH, also require lipoylation for their activity (Mooney et al, 2002;Taylor et al, 2004). Therefore, the observed features of mtkas mutants indicate significant residual activities of all three multienzyme complexes and point to the possibility that mitochondrial protein lipoylation may not be exclusively dependent on mtKAS.…”

Euglena gracilis Rhodoquinone:Ubiquinone Ratio and Mitochondrial Proteome Differ under Aerobic and Anaerobic Conditions

“…These accessory proteins are apparently lacking in bacterial PDH where regulation occurs through allosteric mechanisms and product inhibition (54). The E1 protein of PDH from mitochondria and from Gram-positive bacteria is composed of two different subunits (E1␣ and E1␤), which form an ␣ 2 ␤ 2 heterotetramer (52,55). In contrast, the E1 protein in many Gram-negative bacteria is organized as a homodimer of translationally fused ␣ and ␤ subunits ((␣␤) 2 ) (54,55).…”

CsPDC-E1α, a novel pyruvate dehydrogenase complex E1α subunit gene from Camellia sinensis, is induced during cadmium inhibiting pollen tube growth

“…The plastid form PDCs provide acetyl-CoA and NADH for fatty acid biosynthesis (Lernmark and Gardestrom 1994), whereas the mitochondria form PDCs are important in controlling the entry of carbon into the TCA cycle (Camp and Randall 1985). Most mitochondrial and plastidial proteins, including the subunits of the PDCs, are encoded within the nuclear genome of land plants, synthesized in the cytoplasm and then post-translationally imported into the organelles (Mooney et al 2002). In the present study, CsPDC-E1α was isolated from C. sinensis and phylogenetic analysis of plant PDC-E1α proteins revealed that CsPDC-E1α shares a high degree of homology with PhPDC-E1α (Petunia x hybrida) and VvPDC-E1α (Fig.…”