Reference "The occurrence of riboflavin kinase and FAD synthetase ensures FAD synthesis in tobacco mitochondria and maintenance of cellular redox status"

Reference ID

54977

Title

The occurrence of riboflavin kinase and FAD synthetase ensures FAD synthesis in tobacco mitochondria and maintenance of cellular redox status

Source

FEBS J, 2009, vol. 276, pp. 219-231

Authors (5)

Giancaspero-T-A	Locato-V
de-Pinto-M-C	De-Gara-L
Barile-M

Abstract

Intact mitochondria isolated from Nicotiana tabacum cv. Bright Yellow 2 (TBY-2)
cells can take up riboflavin via carrier-mediated systems that operate at
different concentration ranges and have different uptake efficiencies. Once
inside mitochondria, riboflavin is converted into catalytically active
cofactors, FMN and FAD, due to the existence of a mitochondrial riboflavin
kinase (EC 2.7.1.26) and an FAD synthetase (EC 2.7.7.2). Newly synthesized FAD
can be exported from intact mitochondria via a putative FAD exporter. The
dependence of FMN synthesis rate on riboflavin concentration shows saturation
kinetics with a sigmoidal shape (S(0.5), V(max) and Hill coefficient values 0.32+/-
0.12 microm, 1.4 nmol x min(-1) x mg(-1) protein and 3.1, respectively). The FAD-
forming enzymes are both activated by MgCl(2), and reside in two distinct
monofunctional enzymes, which can be physically separated in mitochondrial
soluble and membrane-enriched fractions, respectively.