Possible component of 1,2-phenylacetyl-CoA epoxidase multicomponent enzyme system which catalyzes the reduction of phenylacetyl-CoA (PA-CoA) to form 1,2-epoxyphenylacetyl-CoA. The subunit D may have a function related to the maturation of the monooxygenase complex, rather than direct involvement in catalysis. PaaD could assist either in maturation of PaaE or PaaA. Aromatic compound metabolism; phenylacetate degradation. Monomer. Activated by cAMP receptor protein (CRP), integration host factor (IHF) and by phenylacetyl-coenzyme A (PA-CoA) that prevents PaaX from binding its target sequences. Inhibited by PaaX. PaaD component is not essential for the reaction in vitro. Extended N-terminus.