On the role of the inducer in the synthesis of maltase in yeast.

One aspect of the process of the induced synthesis of enzymes which is relatively amenable to experimental analysis is the role of the inducer. It has been established in a variety of cases that utilizability is not a necessary attribute of effective inducers. Thus, Spiegelman et al. (1947) demonstrated that maltose can induce maltase at pH values that preclude metabolism of the maltose by fully adapted yeast cells. Analogues of natural substrates have been employed for similar purposes. Thus, a-methyl glucoside can be shown to be an inducer of maltase at concentration levels at which utilization cannot be detected (Spiegelman, 1948). Monod et al. (1951) have demonstrated similarly that melibiose, though not metabolizable by Escherichia coli, is nevertheless an extremely powerful inducer of,-galactosidase. Such experiments eliminated interpretations of inducer function which demand active and detectable metabolic transformations of the inductor, such as might be required were induction to involve the accumulation of unique intermediates derived from the inducer, in the sense suggested by Leibowitz and Hestrin (1945). The data do not exclude mechanisms which involve the conversion or fixation of a very small number of inducer molecules. More pertinent to the purposes of the present paper, however, is the fact that these experiments leave open the question of whether inducers must form complexes, with the enzyme being formed as a sina qua non of induced synthesis of enzyme. Much of the earlier and even some of the more recent (Mandelstam, 1952; Mandelstam and Yudkin, 1952) speculations on the role of the inducer have assumed such complex formation