ABSTRACT
Given a mutual interdependence of cellular structure and protein function, and in view of the fact that protein function must be responsive to altered cellular needs, it follows that the structural framework of the cell must itself be dynamic. There are, obviously, limitations on this structural plasticity, in that many cellular structures such as the mitochondria or endoplasmic reticulum surely possess a permanence that contrasts markedly with the frequently rapid changes that might occur in metabolism. The term "ambiquitous" has been proposed as an adjective describing enzymes whose intracellular distribution may vary with metabolic status, reflected by the levels of certain metabolites capable of influencing that distribution. Allostery, phosphorylation/dephosphorylation and responsiveness to adenylate energy charge, are but some of the factors thought to influence enzymatic activity in vivo. Experimental support for the proposed ambiquitous behavior of brain hexokinase has come from several laboratories.
