Microbiological determination of cystine, systeine, and glutathione in plasma.

In previous reports from this laboratory, a method for the assay of Dand L-methionine in biologic fluids with Leuconostoc mesenteroides P-60 and Lactobacillus fermenti 36 has been described (1, 2). The present communication describes a method for the determination of cysteine plus cystine in plasma. In a report by other workers, using the medium of Dunn et al. (3), the organisms Lactobacillus brewis (8257),’ Lactobacillus pentoaeeticus (367),’ Lactobacillus bwhneri, Lactobucillus lycopersici (4005),’ Leuconostoc mesenteroides P-60 (8042),’ and Leuconostoc dextran,icum (8359)’ have been described as requiring cysteine or cystine for adequate growth. These organisms have been methodically evaluated by us in a variety of additional media, including fortified peroxide-treated gelatin or casein hydrolysate (1,2), the medium of Henderson and Snell (4), and that of Steele et al. (5). Only L. lycopersici and L. bucki have been found to be satisfactory for quantitative determination of these amino acids under the conditions to be described.