Abstract

On the basis of a comparison of the molecular weights and other properties of dehydrogenases it has been suggested that they are all composed of subunits of molecular weights between 17,000 and 21,000. Only certain given numbers of subunits appear to be able to form enzymes. This fact is used to propose quaternary structures for the molecules. A physical model for the interaction between subunits is proposed according to which there is at most one specific point of interaction between neighbouring subunits. All other forces are unspecific and symmetrically distributed around the subunit. Structures are proposed for the α-unit of glutamic dehydrogenase and the pyruvate and α-ketoglutarate decarboxylation complexes consistent with the proposed model and with the assumption that they have icosahedral symmetry. The dissociations, molecular weights, and compositions of these entities can be explained on this basis. It is shown that if virus shells having cubic symmetry are built according to the principles suggested here they will always have icosahedral or pseudo-icosahedral symmetry, and be based on the P = 1 or P = 3 icosadeltahedra, in aggreement with experimental findings to date. Assuming that the active site of a dehydrogenase spans two subunits, and using a slightly modified version of the model already suggested, the number of active sites per enzyme molecule can be predicted. The predictions agree fairly well with experimental evidence to date. Some aspects of in vitro complementation of mutant forms of dehydrogenases are discussed.

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