PT  - JOURNAL ARTICLE
AU  - Anderson, Marc D.
AU  - Che, Ping
AU  - Song, Jianping
AU  - Nikolau, Basil J.
AU  - Wurtele, Eve Syrkin
TI  - 3-Methylcrotonyl-Coenzyme A Carboxylase Is a Component of the Mitochondrial Leucine Catabolic Pathway in Plants
AID  - 10.1104/pp.118.4.1127
DP  - 1998 Dec 01
TA  - Plant Physiology
PG  - 1127--1138
VI  - 118
IP  - 4
4099  - http://www.plantphysiol.org/content/118/4/1127.short
4100  - http://www.plantphysiol.org/content/118/4/1127.full
SO  - Plant Physiol.1998 Dec 01; 118
AB  - 3-Methylcrotonyl-coenzyme A carboxylase (MCCase) is a mitochondrial biotin-containing enzyme whose metabolic function is not well understood in plants. In soybean (Glycine max) seedlings the organ-specific and developmentally induced changes in MCCase expression are regulated by mechanisms that control the accumulation of MCCase mRNA and the activity of the enzyme. During soybean cotyledon development, when seed-storage proteins are degraded, leucine (Leu) accumulation peaks transiently at 8 d after planting. The coincidence between peak MCCase expression and the decline in Leu content provides correlative evidence that MCCase is involved in the mitochondrial catabolism of Leu. Direct evidence for this conclusion was obtained from radiotracer metabolic studies using extracts from isolated mitochondria. These experiments traced the metabolic fate of [U-14C]Leu and NaH14CO3, the latter of which was incorporated into methylglutaconyl-coenzyme A (CoA) via MCCase. These studies directly demonstrate that plant mitochondria can catabolize Leu via the following scheme: Leu → α-ketoisocaproate → isovaleryl-CoA → 3-methylcrotonyl-CoA → 3-methylglutaconyl-CoA → 3-hydroxy-3-methylglutaryl-CoA → acetoacetate + acetyl-CoA. These findings demonstrate for the first time, to our knowledge, that the enzymes responsible for Leu catabolism are present in plant mitochondria. We conclude that a primary metabolic role of MCCase in plants is the catabolism of Leu. BCKDHbranched-chain keto-acid dehydrogenaseDAPdays after plantingHMG-CoA3-hydroxy-3-methylglutaryl-CoAIV-CoAisovaleryl-CoAα-KICα-ketoisocaproateMCCase3-methylcrotonyl-CoA carboxylaseMC-CoA3-methylcrotonyl-CoAMG-CoA3-methylglutaconyl-CoA