Acidic peptides of the lens.
The occurrence in lens extracts of acidic peptides, apparently derived from glutathione, was described in the first paper of this series (Waley, 1956). These compounds were isolated by electrophoresis; they migrated rapidly towards the anode at pH 4 (the 'fast-acid' fraction). A major constituent of this fraction (called lo4) was shown to have glutamic acid as the N-terminal amino acid of a tripeptide, which gave also cystine and glycine on hydrolysis. This paper describes further work leading to the identification of this derivative as the thiosulphate related to glutathionine; following the suggestion of Swan (1957), the thiosulphate will be called Ssulphoglutathione. The main analytical technique employed has been ion-exchange chromatography; S-sulphoglutathione is the most acidic ninhydrinpositive compound in lens extracts and can be readily isolated by using a buffer of high ionic strength so that all the other compounds are barely retarded. EXPERIMENTAL