[Amino acid composition and proton capacity of pea chloroplast thylakoid membranes]

The amino acid composition and pH dependence of proton capacity of pea chloroplast thylakoid membranes have been studied. The thylakoid membranes possess a high content of amino acids, whose functional groups can either bind or split off protons depending on pH of the reaction mixture. The number of amino acids with proton-accepting functional groups per mg of chlorophyll significantly exceeds the proton capacity of the native membranes. It is concluded that the buffer capacity of thylakoid membranes is predetermined by the proton-accepting groups of protein components which are largely blocked within the native structure of the membranes. The protein/chlorophyll weight ratio for pea chloroplast thylakoid membranes is 3.22 +/- 0.05.