The terminal decline of a-amylase (Fig. 8.10) occurs partly because the
reserve protein in the aleurone cells, which provides the amino acids for enzyme
synthesis, is eventually depleted. This cannot be the complete story, however, if
only because of the different kinetics of the increase and decline of the high- and
low-pi groups (Fig. 8.10C). Factors other than amino acid availability obviously
are operating, but we do not yet understand what these are.