Dallas G. Cross

Spectrophotometric studies of the quaternary structure of proteins: I. Method of concentration-difference spectra

Abstract A method is presented for determining effects of concentration-dependent structural changes on environment of chromophoric residues of proteins. The theory for this technique of “concentration-difference spectra” is developed; the experimental methods required for application of that theory are described, and the theoretical effects of certain important experimental errors are considered. An experimental criterion for establishing the validity of a concentration-difference spectrum is proposed. Examples of application of the theory, method, and validity criterion to a dissociable protein system are demonstrated.

Spectrophotometric studies of the quaternary structure of proteins: II. The α, β split of glutamic dehydrogenase☆

Abstract The method of “concentration-difference spectra” was used to study the α, β (dilution) dissociation of the glutamic dehydrogenase molecule. It was found that no phenylalanyl, tryptophanyl, or tyrosyl residues undergo a change in environment in the course of the α, β split. This is in sharp contrast to the α, δ split (to individual peptide chains), which has previously been shown to be due to the breaking of tyrosyl, side-chain-carboxyl, hydrogen bonds, which leads necessarily to a change in environment of tyrosyl residues. The absence of such changes in the α, β split proves that tyrosyl-hydrogen bonds are not involved in holding the individual β subunits together in the intact α molecule.