Isolation and characterization of a glycine transport mutant in an established mammalian cell line, CHO(PEOT/1)

Glycine uptake in CHO(PEOT/1) cells is mediated by at least three systems, of which two have been identified and partially characterized in this study: (1) a low affinity "A" system that transports a number of small neutral amino acids including glycine and methylaminoisobutyric acid (MeAIB), and (2) a high-affinity system, specific for glycine and sarcosine. By a combination of tritium suicide and replica plating, we have isolated a mutant (CHY-3) with a 47% decrease in glycine transport at the standard test concentration of 2.5 microM. Uptake studies with radioactive glycine, MeAIB, and sarcosine revealed that the mutant lacks the glycine-sarcosine system, but has undergone a compensatory 30-50% increase in the A system. Thus, there appears to be a regulatory interaction between these two systems for glycine uptake by CHO cells.