Fig 1.

Reactions of the proposed reductive pathway for 3-hydroxypropionate assimilation by Rhodobacter sphaeroides 2.4.1. Acrylyl-CoA reductase (AcuI) is encoded by RSP_1434 (shown in the box). The reactions indicated by the dotted arrows are hypothetical; however, at least part of these reactions should exist, based on the fact that the overall conversion of 3-hydroxypropionate or acrylate to propionyl-CoA can be measured in cell extracts as described previously (14). In the case of R. sphaeroides, propionyl-CoA is assimilated via the methylmalonyl-CoA pathway and enters the citric acid cycle at succinyl-CoA. The methylmalonyl-CoA pathway consists of the following enzymes: propionyl-CoA carboxylase (alpha and beta subunits encoded by RSP_2191 and RSP_2189, respectively), ethylmalonyl-CoA/methylmalonyl-CoA epimerase (encoded by RSP_0812), and (2R)-methylmalonyl–CoA mutase (encoded by RSP_2192).