Inhibition of the Photosynthetic Electron Transport of Isolated Chloroplasts by Hemolyzed Rabbit Sera

Abstract

The photosynthetic reduction of oxygen, which leads to the formation of hydrogen peroxide (H2O2) and a consequent net consumption of oxygen (O2) was first discovered by Mehler [1], This reaction has since been termed the “Mehler reaction.” it has been accepted that MV and Fd accept electrons from the primary electron acceptor of PSI (X), refered to as ferredoxin reducing substance (FRS), before transfering an electron to oxygen or NADP [2]. Recent developments in research on the primary electron acceptor of PSI, have shown that a series of electron acceptors is involved before the reduction of Fd [3]. The primary electron acceptor from P700 may be a monomeric chlorophyll anion designated A0 -. Electron transfer probably proceeds to a semiquinone (A1-). The electron acceptors following A1- are three iron sulfur (Fe-S) centers denoted as Fx, Fa and FX. It is still unresolved whether these Fe-S centers act in series or in parallel. The experimental evidence tends to favor the concept that electron transfer to the Fe-S centers, particularly Fa and Fb, is in parallel under physiological conditions. It is not known which one of these electron acceptors (ie. Fx, Fa, Fb) interacts with Fd and MV in the reduction of O2. It may be possible that parallel electron flow has a significant role in a differential reduction of NADP and O2 by Fd. in this communication, we report on the patterns of inhibition of photosynthetic electron transport by an unknown inhibitor from hemolyzed rabbit sera that supports the concept of parallel electron flow. A tentative model is proposed to explain the interaction of the Mehler reaction with PSI.