Subunit Structure of L‐Lactate Dehydrogenase (Cytochrome b 2 ) of Saccharomyces cerevisiae
1972; Wiley; Volume: 25; Issue: 2 Linguagem: Inglês
10.1111/j.1432-1033.1972.tb01691.x
ISSN1432-1033
Autores Tópico(s)Protein Structure and Dynamics
ResumoThe molecular weights of yeast L‐lactate dehydrogenase (cytochrome b 2 ) and of its polypeptide chains have been measured by ultracentrifugation. The intact protein was found to have a molecular weight of 240000 ± 10000 by sedimentation equilibrium measurements according to the Yphantis high‐speed method. The solution obtained by dissolving the protein in 6 M guanidine (with added 2‐mercaptoethanol) behaved as if it were monodisperse, giving M r = 31300 ± 2000, by approach‐to‐equilibrium measurements. This result indicates that the “58 600 unit” associated to one set of prosthetic groups, heme and flavin, is made up of two chains, and thus the whole molecule contains a total of eight chains, identical or not. However, as the viscosity of the medium was reduced (using 2 M guanidine) the paucidispersity of the cytochrome b 2 solution was revealed. The mixture was shown to consist of two kinds of chains distinct in molecular weight. From these experiments the molecular weight of the light chain was found to be 22600 ± 1500. After partial separation of the two chains by gel filtration through Sephadex G‐100, the molecular weight of the heavy chain was estimated as 39700 ± 3000. Preliminary experiments indicate that the heavy component can bind quantitatively the heme prosthetic group. The FMN appears to be bound to the light component.
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