Carboxyl‐terminal processing may be essential for production of active NiFe hydrogenase in Azotobacter vinelandii

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Abstract
The NiFe hydrogenase from Azotobacter vinelandii is a membrane-bound αβ heterodimer that can oxidize H2 to protons and electrons and thereby provide energy. Genes encoding the α and β subunits, hoxG and hoxK respectively, followed by thirteen contiguous accessory genes potentially involved in H2 oxidation, have been previously sequenced. Mutations in some of these accessory genes give rise to inactive enzyme containing an α subunit with decreased electrophoretic mobility. Mass spectral analysis of the subunits demonstrated that the α subunit had a molecular weight 1,663 Da less than that predicted from hoxG. Since the N-terminal sequence of the purified α subunit matches the sequence predicted from hoxG we suggest this difference is due to removal of the C-terminus of the α subunit which may be an important step linked to metal insertion, localization, and formation of active hydrogenase.