Weitere Untersuchungen über den Einbau von radioaktivem Schwefel in Blattproteine von Ölrettichpflanzen

Further investigations upon the 35 S‐incorporation into some leaf proteins of oil radish plants . In order to supplement earlier results, concerning the 35 S‐incorporation into leaf proteins of oil radish plants, a new experiment with increasing amounts of 35 S‐labelled sulphate‐sulphur was started under controlled climatic conditions. The 35 S‐incorporation into some protein fractions was determined by methods of gel chromatography with various types of Sephadex, by the isoelectric focusing and the liquid scintillation counting. Fresh weights and content of pure protein of the plants were scarcely influenced by increasing amounts of sulphur supplied. In the S‐variants 2 and 3 an increased relative incorporation of sulphur from the sulphur fertilization was observed in nitrogen‐ and sulphurcontaining compounds with lower molecular weights (m.w. < 4000) and into some protein fractions, especially with molecular weights, higher than 4–8 X10 5 (Sephadex G‐200). Determination of total 35 S‐activity in the leaf material has shown, that the plants of all S‐variants have taken up sulphur in nearly equal proportions. Therefore, a pronounced S‐incorporation into some protein fractions must have taken place. It is assumed, that the 35 S‐marked compounds with lower molecular weights are final products, and the 35 S‐marked protein fractions with higher molecular weights may be enzymes of the secondary sulphur metabolism, the activity of which has probably been intensified in plants, supplied with higher amounts of sulphur. Comparing the earlier and the present investigations, it must be pointed out, that there are some differences in the results of protein fractionation and 35 S‐patterns, probably caused by a varied performance of these experiments. Nevertheless, similar tendencies may be pointed out in the high rate of S‐incorporation into protein fractions.