Daniel Arnon and coworkers carried out experiments with intact, saltwashed chloroplasts to study photophosphorylation. When the chloroplasts were illuminated in the presence of ADP + P_i , ATP was produced, but oxygen was not produced nor consumed. ATP formation was not accompanied by a measurable electron transport involving any external electron donor or acceptor. The overall reaction for this result is:

When NADP⁺ was included in addition to the ADP + P_i , illumination of the intact chloroplasts again resulted in the photophosphorylation of ADP to ATP. In addition, the NADP⁺ was reduced to NADPH + H⁺, and O₂ was produced. Moreover, the light-induced reduction of NADP⁺ was greatly decreased if ADP + P_i was omitted. The equation for this reaction is:

Briefly describe the mechanism (s) of these two types of photophosphorylation that explain all of these results 

Transcribed Image Text:

ADP + P₁ hv ATP