Clues to the origin of high external invertase activity in immobilized growing yeast: prolonged SUC2 transcription and less susceptibility of the enzyme to endogenous proteolysis

Expression of the SUC2 gene encoding invertase was studied using free and g elatin-immobilized yeast cells to try to explain the high activity of this enzyme exhibited by immobilized cells when allowed to grow in a nutrient me dium. The results indicated that at least two factors are probably responsi ble for the accumulation of invertase in immobilized cells. First, the expr ession of the SUC2 gene was maintained throughout growth in immobilized cel ls, whereas its expression was only transient in free cells. Second, invert ase of immobilized cells was shown to be less susceptible to endogenous pro teolytic attack than that of the corresponding free cells. These results ha ve been interpreted, respectively, in terms of diffusional limitations and changes in the pattern of invertase glycosylation due to growth of yeast in an immobilized state.