Carnitine acyltransferases in chloroplasts of Pisum sativum L.

Mclaren, I.; Wood, C.; Jalil, Muhammad; Yong, Bob C. S.; Thomas, David

doi:10.1007/bf00393506

Cited by 26 publications

(11 citation statements)

References 20 publications

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“…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.…”

Section: Discussionmentioning

confidence: 99%

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

Lernmark

Gardeström

1994

Plant Physiol.

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Protoplasts from barley (Hordeum vulgare), pea (fisum sativum), wheat (Trificum aesfivum), and spinach (Spinacia oleracea) leaves were fradionated into chloroplast-and mitochondrionenriched fractions. Pyruvate dehydrogenase complex capacities in mitochondria (mtPDC) and chloroplasts (cpPDC) were measured in appropriate fractions under conditions optimal for each isozyme. The total cellular capacity of PDC was similar in barley and pea but about 50% lower in wheat and spinach. In pea a distribution of 87% mtPDC and 13% cpPDC was found on a cellular basis. In barley, wheat, and spinach the subcellular distribution was the opposite, with about 15% mtPDC and 85% cpPDC. cpPDC adivity was constant at about 0

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Section: Discussionmentioning

confidence: 99%

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

Lernmark

Gardeström

1994

Plant Physiol.

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“…The results rule out the conservation of the thioester bond during acyl export from the plastid, either directly (even if driven by ATP-dependent process to make it directional) or by a "high-energy" intermediate such as acyl-carnitine. An argument has been made that the conservation of the energy of the thioester bond would be preferable during fatty acid export (Thomas et al, 1982(Thomas et al, , 1983McLaren et al, 1985). Countering this argument, it should be noted that the expenditure of an additional ATP in the synthesis of a C18 fatty acid that requires on a molar basis 8 mol of ATP and 16 mol of NAD(P)H for synthesis from acetyl-CoA is not great.…”

Section: Eukaryotic Lipid Synthesis Proceeds With a Hydrolyticmentioning

confidence: 99%

“…Thomas and co-workers have suggested that fatty acyl groups may be exported from the plastid as acyl carnitines (Thomas et al, 1982(Thomas et al, , 1983McLaren et al, 1985). In addition, an acyl-CoA thioesterase was observed with chloroplast envelopes (Joyard and Stumpf, 1980) and was later more specifically localized to the inner envelope (Andrews and Keegstra, 1983;Block et al, 1983).…”

mentioning

confidence: 99%

Testing Models of Fatty Acid Transfer and Lipid Synthesis in Spinach Leaf Using in Vivo Oxygen-18 Labeling

Pollard

Ohlrogge

1999

Plant Physiology

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“…Spots scraped from the TLC plate were counted in 10 ml Optiphase scintillant for 10 min. The identity of the acetylcarnitine spot was con¢rmed by TLC with an authentic standard and by mass spectrometry as described by McLaren et al (1985).…”

Section: (D) Assaysmentioning

confidence: 99%

Pea chloroplast carnitine acetyltransferase

Masterson

Wood

2000

Proc. R. Soc. Lond. B

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The purpose of this study was to resolve the controversy as to whether or not chloroplasts possess the enzyme carnitine acetyltransferase (CAT) and whether the activity of this enzyme is su¤cient to support previously reported rates of fatty acid synthesis from acetylcarnitine. CAT catalyses the freely reversible reaction: carnitine + short-chain acylCoA 6 short-chain acylcarnitine + CoASH. CAT activity was detected in the chloroplasts of Pisum sativum L. With membrane-impermeable acetyl CoA as a substrate, activity was only detected in ruptured chloroplasts and not with intact chloroplasts, indicating that the enzyme was located on the stromal side of the envelope. In crude preparations, CAT could only be detected using a sensitive radioenzymatic assay due to competing reactions from other enzymes using acetyl CoA and large amounts of ultraviolet-absorbing materials. After partial puri¢cation of the enzyme, CAT was detected in both the forward and reverse directions using spectrophotometric assays. Rates of 100 nmol of product formed per minute per milligram of protein were obtained, which is su¤-cient to support reported fatty acid synthesis rates from acetylcarnitine. Chloroplastic CAT showed optimal activity at pH 8.5 and had a high substrate speci¢city, handling C2^C4 acyl CoAs only. We believe that CAT has been satisfactorily demonstrated in pea chloroplasts.

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Carnitine acyltransferases in chloroplasts of Pisum sativum L.

Cited by 26 publications

References 20 publications

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

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

Testing Models of Fatty Acid Transfer and Lipid Synthesis in Spinach Leaf Using in Vivo Oxygen-18 Labeling

Pea chloroplast carnitine acetyltransferase

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