PLANT PHYSIOLOGY , Vol 108, Issue 3 1133-1139, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Regulation of [beta]-Methylcrotonyl-Coenzyme A Carboxylase Activity by Biotinylation of the Apoenzyme
X. Wang, E. S. Wurtele and B. J. Nikolau
Department of Biochemistry and Biophysics (X.W., B.J.N.) and Department of Botany (E.S.W.), Iowa State University, Ames, Iowa 50011
Regulation of the expression of the gene(s) coding for the 78-kD,
biotin-containing subunit of [beta]-methylcrotonyl-coenzyme A carboxylase
(MCCase) was investigated in different organs of tomato (Lycopersicon
esculantus) plants. The specific activity of MCCase is highest in extracts
from roots, followed in descending order by ripe and ripening fruits,
stems, and leaves. The specific activity is 10-fold higher in roots than in
leaves. However, the steady-state levels of the 78-kD subunit of MCCase and
its mRNA are approximately equal in both roots and leaves. Instead, the
difference in MCCase activity between these two organs is directly
correlated to the biotinylation status of the enzyme's biotin-containing
subunit. Thus, the lower activity of MCCase in leaves is attributed to the
reduced biotinylation of the biotin-containing subunit of the enzyme.
Consistent with this model, a pool of nonbiotinylated enzyme is present in
leaves, whereas the nonbiotinylated enzyme is undetectable in roots. The
underbiotinylation of MCCase in leaves is not due to a lack of biotin in
this organ, since the biotin concentration is 4- to 5-fold higher in leaves
than in roots. These observations indicate that the posttranslational
biotinylation of the biotin-containing sub-unit of MCCase is an important
mechanism for regulating the organ-specific expression of MCCase activity.
