Separation of Two Forms of Anthranilate Synthetase from 5‐Methyltryptophar Susceptible and ‐Resistant Cultured Solarium tuberosumCells

Potato cell suspension cultures (Solanum tuberosumL. cv. Merrimack) have been selected which are resistant to growth inhibition by D,L‐5‐methyltryptophan. Anthranilate synthetase activity in crude extracts from resistant cells was less sensitive to feedback inhibition by L‐tryptophan and D,L‐5‐methyltryptophan than the activity from the sensitive line. This altered feedback control apparently accounts for the cell's resistance to growth inhibition since there is a 48‐fold increase in free tryptophan in one of the resistant cell lines. Preparative polyacrylamide gel electro‐phoresis separated feedback‐sensitive and ‐resistant forms of anthranilate synthetase in extracts from both 5‐methyltryptophan‐susceptible and ‐resistant cells, with a predominance of the corresponding form in the respective cell type. The anthranilate synthetase activity from the 5‐methyltryptophan‐resistant line was inactivated more slowly by incubation of crude extracts at 50°C than the activity from the sensitive line. These results suggest the presence of two isoenzymes of anthranilate synthetase in cultured potato cells.