<p>Escherichia coli NADPH-sulphite reductase (SiR) is a multimeric hemoflavoprotein composed of eight alpha-subunits (SiR-FP) and four beta-subunits (SiR-HP) that catalyses the six electron reduction of sulphite to sulphide. This is one of several activities required for the biosynthesis of L-cysteine from sulphate. The alpha component of NADPH-sulphite reductase is a flavoprotein, the beta component is a hemoprotein [<cite idref="PUB00014351"/>]. The flavoprotein component catalyses the electron flow from NADPH to FAD to FMN to the hemoprotein component.</p><p>This entry describes an NADPH-dependent sulphite reductase flavoprotein subunit alpha. It binds one FAD and one FMN as prostheticgroups and contains an NADPH-binding domain [<cite idref="PUB00014352"/>]. </p> Sulphite reductase [NADPH] flavoprotein, alpha chain