SUPRAMOLECULAR ASSOCIATIONS WITH THE CYTOMATRIX AND THEIR RELEVANCE IN METABOLIC CONTROL - PROTEIN-SYNTHESIS AND GLYCOLYSIS

Cytoplasm is structured by supramolecular associations between cytoske letal elements, metabolites, ions, and enzymes. Since the molecules ar e not distributed homogenously, whole cell concentrations have little meaning, and high local concentrations may be reached in cells showing overall low contents. Biochemical reactions in living cells differ fr om those in the test tube by high protein concentrations and low overa ll substrate concentrations. The high molecular density (crowding) of cytoplasm influences macromolecular associations which may form the ba sis for metabolite channeling. This is discussed in relation to (i) th e function-structure relationship of the translational apparatus and i ts binding to the cytomatrix, and (ii) the physiological significance of the association of glycolytic enzymes to actin and microtubules. Th us, glycolytic enzymes and factors involved in the control of transcri ption and translation may exert catalytic functions and may be involve d in the generation of subcellular structures. Both these activities a re supposed to be related reciprocally with each other. Several factor s located in the cytoplasm and in the nucleus as well seem to particip ate in a complicated network controlling differentiation and growth. C onsequently, a new understanding of the dynamic structure of cytoplasm has emerged, emphasising the continuity from single molecules to the whole organism by weak bond interactions which are essential system pr operties of organisms, overruling a strict reductionistic mode of desc ription. For further precision of this view, biochemical experimentati on has to be extended to studies of living cells using physicochemical approaches which allow the monitoring of transient activity changes a nd supramolecular associations.