Molecular compartmentation by enzyme cluster formation

Abstract

Current investigations in different fields of cellular metabolism focus on the phenomenon of molecular compartmentation as an essential part of metabolic control. This type of compartment without surrounding membranes arises from enzyme cluster formation in the cell. The organization of the enzymes ranges from very loose, non-covalent aggregations, sometimes only transiently associated - dependent on metabolic or developmental state of the cell - to the very fixed, even covalently linked structures. These organized multienzyme systems produce a chemical microheterogeneity concerning the metabolite concentrations in the cell. Molecular compartmentation is the description of this chemical microheterogeneity in a biological term.

Phase separation in cytoplasm, due to macromolecular crowding, is the basis for microcompartmentation

“…coenzyme) [21] and ~rotein-protein (e.g. enzyme clusters as in the glycolytic com-)lex) [9,22,23] binding have all been observed 'compartmentalzed' in cytoplasm. Glycogen, a branched polysaccharide, could yell produce phase separation with some proteins, providing t microphase in which the degradative reactions of glycolysis md the synthesis of glycogen occur.…”

“…of enzymes in a spe-:ific metabolic sequence) result in complexes which partition lifferently from the individual components [24], providing a ocalization mechanism. Thus, compartmentation of metabolic ,equences [6,22] in cytoplasm (and the channeling of intermedittes [25]) can result from partitioning into a specific micro~hase. Reaction products of the polymer phase-'immobilized' ,~nzyme complexes, being smaller, generally partition more :qually, reducing thereby biofeedback effects [3].…”

“…Protein-protein interactions [9,22,23]. Altered protein distribution due to reaction with small molecule and conformational change [9].…”

“…Compartmentation of metabolism [6,22] and channeling of intermediate [25]. Non-ideal, slow diffusion of micro-[29,30] and macromolecules [5,7,27,31 33] and particulates [34].…”

A Specific Association Between the Glyoxylic‐Acid‐Cycle Enzymes Isocitrate Lyase and Malate Synthase

“…In recent years it was realized that the aqueous-phase properties in the interior of a cell seem to be essentially different from those of an ordinary aqueous solution Clegg, 1984;Friedrich, 1986;Keleti et al, 1989;Srere, 1987;Bernhard, 1986, 1987;Wombacher, 1983). It was calculated that protein concentrations in various subcellular compartments may be as high as 0.5 g/ml, which is comparable to the protein concentration in enzyme crystals (Fulton, 1982 ;Hackenbrock, 1968 ;Srere, 1980).…”