1.3.1.33 chlorophyllide a + NADP+ = protochlorophyllide + NADPH + H+ catalytic mechanism suggested: protochlorophillide absorbs a photon, creating a transient charge separtaion across the C17-C18 double bond, which promotes ultrafast hydride transfer from the pro-S face of NADPH to the C17 of protochlorophillide. The resulting A696 charge transfer intermediate facilitates transfer of a proton to the C18 of protochlorophillide during the subsequent first dark reaction 674637 1.3.1.33 chlorophyllide a + NADP+ = protochlorophyllide + NADPH + H+ light - 1.3.1.33 chlorophyllide a + NADP+ = protochlorophyllide + NADPH + H+ The enzyme catalyses a light-dependent trans-reduction of the D-ring of protochlorophyllide. The product has the (7S,8S)-configuration -