Abstract
l-2,5-Dihydrophenylalanine is extensively incorporated as a phenylalanine analogue into cell proteins. Phenylalanine-requiring Escherichia coli ATCC 9723f and sarcoma 180 grow at normal rates initially with the analogue and maximally replace 65 and 33%, respectively, of phenylalanine in the peptide residues of their cell protein without death. With the analogue alone growth of E. coli becomes non-steady-state and asymptotically inhibited. In mixtures of the analogue and phenylalanine, growth eventually becomes steady state or logarithmic. The logarithmic rate is inversely proportional to the extent of incorporation of this analogue or of p-fluorophenylalanine, and the projected maximal replacement is the same as that obtained asymptotically with the analogue alone. Thus, the toxicities in steady-state and non-steady-state growth are closely related. Moreover, it is proposed that single salient protein defects may determine the extent of growth rate reduction.