On the process of induction of adenosine triphosphate hydrolysis by chloroplasts with cysteine as activating thiol

Abstract

A study of ATP hydrolysis by Class II spinach chloroplasts in the dark following an illumination period in the presence of cysteine has been carried out and a comparison is made with similar results using DTT as the activating thiol. In general ATP hydrolysis in the presence of NH 4 + is shown to be more sensitive than in the absence of NH 4 + to variations in the induction efficiency. With PMS as added cofactor a pink compound results by interaction with cysteine. The results indicate that this pink compound participates in an electron transfer sequence giving rise to variations in the efficiency of induction according to its concentration and rate of reoxidation. With FMN as cofactor removal of O 2 from the bulk phase of the mixture by cysteine results in a shortage of the oxidized form of FMN for electron transfer reactions unless the mixture is stirred. This again affects the efficiency of induction and provides evidence for the involvement of electron transfer reactions. The actions of DCMU further substantiate these conclusions. Mg 2+ ions need not always be added during induction the requirement depending on the experimental conditions. The process of induction is discussed in the light of the chemical and chemiosmotic hypotheses for energy transfer.