Carnitine acetyltransferase in pea cotyledon mitochondria

Abstract

Purified pea cotyledon mitochondria did not oxidise acetyl-CoA in the presence of carnitine. However, acetylcarnitine was oxidised. It was concluded that acetylcarnitine passed through the mitochondrial membrane barrier but acetyl-CoA did not. Only a sensitive radioactive assay detected carnitine acetyltransferase in intact mitochondrion or intact mitoplast preparations. When the mitochondria or mitoplasts were burst, acetyl-CoA substrate was available to the matrix carnitine acetyltransferase and a high activity of the enzyme was measured. The inner mitochondrial membrane is there-fore the membrane barrier to acetyl-CoA but acetylcarnitine is suggested to be transported through this membrane via an integral carnitine: acylcarnitine translocator. Evidence is presented to indicate that when the cotyledons from 48-h-grown peas are oxidising pyruvate, acetylcarnitine formed in the mitochondrial matrix by the action of matrix carnitine acetyltransferase may be transported to extra-mitochondrial sites via the membrane translocator.

Reverse Genetic Characterization of Cytosolic Acetyl-CoA Generation by ATP-Citrate Lyase in Arabidopsis

“…Overall, our observations imply that ACL is near-limiting in generating cytosolic acetyl-CoA and that other mechanisms (Wood et al, 1983;Burgess and Thomas, 1986;Masterson et al, 1990) for generating cytosolic acetyl-CoA cannot substitute for ACL-derived acetyl-CoA.…”

“…By distributing this metabolism among separate cellular and subcellular compartments, plants have the potential of simplifying the regulatory processes that control this complex network. Although the generation of plastidic acetyl-CoA as the precursor for fatty acid biosynthesis has been the focus of considerable research (Millerd and Bonner, 1954;Nelson and Rinne, 1975;Reid et al, 1975;Kuhn et al, 1981;Kaethner and ap Rees, 1985;Burgess and Thomas, 1986;op den Camp and Kuhlemeier, 1997;Ke et al, 2000;Schwender and Ohlrogge, 2002), few studies have directly addressed the question of how the cytosolic (Kaethner and ap Rees, 1985;Fatland et al, 2002;Schwender and Ohlrogge, 2002) or nuclear acetyl-CoA pools are generated. This is despite the fact that most of the chemical diversity of acetate-derived molecules is generated from the cytosolic acetyl-CoA pool.…”

Distribution of Pyruvate Dehydrogenase Complex Activities between Chloroplasts and Mitochondria from Leaves of Different Species

“…This acetate could be synthesized in the mitochondria by the combined action of mtPDC and an acetyl-COA hydrolase (Murphy and Stumpf, 1981;Zeiher and Randall, 1990). Also, acetyl-COA could be shuttled directly between the mitochondria and chloroplasts by a camitine/acetyl camitine exchange system across the mitochondrial (Burgess and Thomas, 1986) and chloroplast (McLaren et al, 1985) inner membranes. The low mtPDC to cpPDC capacity found in barley leaves raises the question of whether enough acetyl-COA is produced by mtPDC to provide substrate for both CS and a possible acetyl-COA hydrolase.…”

Pea chloroplast carnitine acetyltransferase

“…It is suprising that Roughan et al (1993) found no CAT activity in homogenates of pea shoots and spinach and amaranthus leaves as it is fairly well established that mitochondria at least possess CAT activity Wood et al 1983;Burgess & Thomas 1986;Gerbling & Gerhardt 1988;Budde et al 1991) and this mitochondrial CAT should have been detected.…”