The biosynthesis of cystine in human cell cultures.

Cystine is one of five amino acids (arginine, cystine, glutamine, histidine, tyrosine) which are essential for the survival and growth of human and animal cells in culture (l-3), even though they are not needed for nitrogen balance in man. It will here be shown that all the serially propagated human strains so far studied can synthesize cystine from methionine and glucose, but that under ordinary conditions of culture, trace concentrations of exogenous cystine are necessary to prevent its loss from the cells at a faster rate than it can be synthesized, with resulting pool depletion and cellular death.