Genetic Studies on Mutant Enzymes in Maize. IV. Comparison of Ph 7.5 Esterases Synthesized in Seedling and Endosperm.

STUDIES on the genetic control of protein specificity have centered almost exclusively on the control of the primary structure of the protein, i.e. amino acid composition and sequence. Very little is known about what determines the secondary and tertiary structure. Are the secondary and tertiary structures determined completely by the primary structure or are they also dependent upon, and can they be modified by, other factors such as the physiological condition of the cell in which the protein is being synthesized? This paper is concerned with a comparison of an enzyme specified by the same gene functioning in two different tissues of the maize plant. Specifically, the comparison is of the relative inactivation of the pH 7.5 esterases of endosperm and seedling by urea and thioglycolic acid. The enzymes specified by a particular allele in various parts of the plant show no apparent differences in size and charge as determined by electrophoretic mobility in starch gel.