Abstract
In some C4 plant species, a mitochondrial NAD-dependent malic enzyme (EC 1.1.1.39) (NAD-ME) catalyzes the decarboxylation of 4 carbon malate in the bundle sheath cells, releasing CO2 for the Calvin cycle of photosynthesis. In amaranth, a dicotyledonous NAD-ME-type C4 plant, the photosynthetic NAD-ME purified as two subunits of 65 and 60 kDa, designated alpha and beta, respectively. Antiserum raised against the alpha subunit reacted only with the 65-kDa protein in immunoblot analysis. Immunogold electron microscopy using the alpha subunit antiserum demonstrated that this protein was localized specifically to the mitochondrial matrix of bundle sheath cells. The complete nucleotide sequence of a 2300-base pair alpha subunit cDNA clone showed that this gene encodes a protein that contains all of the motifs required for a complete and functional malic enzyme. The alpha subunit has significant similarity along its entire length to other known NAD- and NADP-dependent malic enzymes from plants, animals, and bacteria. The findings presented here provide new insights about the C4 photosynthetic NAD-ME and its evolutionary relationship to other forms of malic enzyme present in eukaryotic and prokaryotic organisms.
Highlights
NAD-Malic enzymes (ME)-typeC4 plant, the photosyntheticNAD-ME in many plant species [14].In most plants it appears to be purified as two subunits of 66 and 60 kDa, designated a and 8, respectively
Thea subunit has significant similarity C4 plant speciespossess a specializedKranz-type leaf anatalong its entire length to otherknownNAD-and omy, which consists of two photosynthetic cell types, the NADP-dependent malic enzymes from plants, animalbsu,ndle sheath and mesophyll cells [8, 9]
Purification and Identification of NAD-dependent malic enzyme (NAD-ME) Proteins-Previous studies of NAD-ME in plants indicate that the active form of this enzyme exists primarily as anoctomer composed of two distinct subunits, a and p, both of which are required for enzymatic activity [3, 13]
Summary
NAD-ME-typeC4 plant, the photosyntheticNAD-ME in many plant species [14].In most plants it appears to be purified as two subunits of 66 and 60 kDa, designated a and 8, respectively. The NADME from amaranth mitochondria purified as two polypeptides, oneof approximately 65 kDa and one of approximately 60 kDa (Fig. LA).These two proteins were present in approximately equal amounts and were similar in size to the a and p subunits of plant mitochondrial NAD-ME as previously
Sign-in/Register to view highlights & summary 
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call