Cystine requirement of continuous human lymphoid cell lines of normal and leukemic origin.

A number of continuous, human lymphoid cell lines from healthy and leukemic donors have been studied. Those from healthy individuals were found to be cystine prototrophs (cys+), while those from leukemic donors were observed to be cystine auxotrophs (cys-). The former can grow in either cystine or cystathionine-containing media. The latter grow only in cystine-containing medium. The former contain readily measurable levels of cystathionase, the last enzyme in the mammalian cysteine biosynthetic pathway, while the latter contain much less of this activity. The apparent molecular weight, overall charge, pH versus activity, Km, and [pyridoxal phosphate] versus activity properties of the enzyme from both cell types were indistinguishable. No soluble cystathionase inhibitor could be detected in cys- cell lines. Thus, it is reasonable to hypothesize that those leukemic cell lines studied synthesize less active cystathionase protein than their cys+ counterparts and that this difference in enzyme production underlies the differential growth properties in cystathionine-containing medium.