Acetyl-CoA carboxylase in higher plants: most plants other than gramineae have both the prokaryotic and the eukaryotic forms of this enzyme.

The presence and the absence of a prokaryote type and a eukaryote type of acetyl-CoA carboxylase (EC 6.4.1.2; ACCase) were examined in members of 28 plant families by two distinct methods: the detection of biotinylated subunits of ACCase with a streptavidin probe, and the detection of the accD gene, which encodes a subunit of the prokaryotic ACCase, by Southern hybridization analysis. The protein extracts of all the plants studied contained a biotinylated polypeptide of 220 kDa, which was probably the eukaryotic ACCase. All the plants but those belonging to Gramineae also contained a biotinylated polypeptide of ca. 35 kDa, which is a putative subunit of the prokaryotic ACCase. In all plants but those in Gramineae, the ca. 35 kDa polypeptide was found in the protein extracts of plastids, while the 220 kDa polypeptide was absent from these plastid extracts. The plastid extracts of the plants in Gramineae contained the 220 kDa polypeptide, as did the homogenates of the leaves. Southern hybridization analysis demonstrated that all the plants but those in the Gramineae contained the accD gene. These findings suggest that most higher plants have the prokaryotic ACCase in the plastids and the eukaryotic ACCase in the cytosol. Only Gramineae plants might contain the eukaryotic ACCases both in the plastids and in the cytosol. The origin of the plastid-located eukaryotic ACCase in Gramineae is discussed as the first possible example of substitution of a plastid gene by a nuclear gene for a non-ribosomal component.