nirD

Summary: This subunit contributes to the native NirBD nitrite-reductase activity.

Reason: The family-specific signature identifies the accessory small subunit. Native KT2440 operon expression and nitrite-reductase activity support its complex context. The ordinary imported relationship label is inert: independent catalysis is not required for a complex contribution. Physiological NADH-versus-NADPH preference is not established by the artificial-donor lysate assay.

Summary: A Rieske-like fold does not establish a canonical 2Fe-2S binding site in NirD.

Reason: The target sequence has Cys18, Cys95, and only one histidine, His87, incompatible with the canonical Rieske two-cysteine/two-histidine ligand set. Independent NirD-specific family membership and the cofactor-free M. tuberculosis NirD structure support a fold-level electronic over-transfer. The structure is comparative, not a native KT2440 cofactor measurement.

Summary: The accessory subunit participates in the assimilatory nitrite-reduction step.

Reason: Retain the inherited process proposal on a structural-component role: NirD belongs to the conserved small-subunit family of the enzyme that executes nitrite reduction. Native operon identity supports this context; the claim is not inferred from generic growth necessity alone. The distinct Y-9 deletion study is comparative support and does not establish KT2440 DNRA. No redundant process ancestor or descendant is proposed.

Summary: NirD is the accessory component of the NirBD complex.

Reason: Retain the inherited conserved-complex inference from the NirD signature, native paired operon, and comparative NirBD structural evidence. Native KT2440 subunit assembly and stoichiometry remain to be tested directly.