FMN (Flavin mononucleotide or riboflavin 5'-phosphate) and FAD (flavin adenine dinucleotide) are mainly located in mitochondria, where they act as redox cofactors of a number of dehydrogenases and oxidases that play a crucial function in both bioenergetics and cellular regulation. In this report, Saccharomyces cerevisiae mitochondria (SCM) competence to metabolise externally added and endogenous FAD and FMN was investigated. Because intact and coupled mitochondria are strictly required to carry out studies concerning mitochondrial metabolism, a series of preliminary experiments was performing using isolated SCM in order to ascertain structural and functional feature (intactness of mitochondrial inner/outer membranes, Respiratory Control, ΔΨ generation). Then, the amounts of flavins in aliquots of neutralized perchloric extracts of both spheroplasts and mitochondria were measured by HPLC SCM capability to metabolise externally added and endogenous FAD and FMN was investigated both spectroscopically and via HPLC. FAD deadenylation and FMN dephosphorylation were studied with respect to following features: dependence on substrate concentration, pH profile and inhibitor sensitivity. The existence of two novel mitochondrial FAD pyrophosphatase (diphosphatase) (EC 220.127.116.11) and FMN phosphohydrolase (EC 18.104.22.168) activities, which catalyse FAD+H2O→FMN+AMP and FMN+H2O→riboflavin+Pi conversion, respectively, is here shown. In the light of cytosolic riboflavin, FMN and FAD concentrations, probably mitochondria play a major role in regulating the flavin pool in yeast cell under glucose limitation and in relation to flavoprotein deflavination and reconstitution. PDF created
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