METABOLISM OF ELEMENTAL SULFUR AND OXIDATION OF SULFITE BY WHEAT AND SPINACH-CHLOROPLASTS

Wheat or spinach chloroplasts were fed with S-35-labelled elemental su lphur (S-0). S-35-labelled compounds appearing thereafter were analyse d. Five S-35-compounds were recovered, thiosulphate, sulphite, sulphat e, cysteine and glutathione. The effect of environmental conditions wa s also studied. The measurement of S-0 metabolism rate was compared to the recovery of the introduced S-0 into other S compounds. The specif ic radioactivity of thiosulphate and sulphate was determined. The resu lts obtained have permitted the elucidation of the precise biochemical pathway of S-0 oxidation. The oxidation of sulphite in wheat and spin ach chloroplasts occurs via both non-enzymatic (in particular the oper ation of the photosynthetic electron transport chain) and enzymatic pr ocesses (sulphite oxidase activity).