ABSTRACT
The solution structure of the protein disulfide oxidoreductase Mj0307 in the reduced form has been solved by nuclear magnetic resonance. The secondary and tertiary structure of this protein from the archaebacterium Methanococcus jannaschii is similar to the structures that have been solved for the glutaredoxin proteins from Escherichia coli, although Mj0307 also shows features that are characteristic of thioredoxin proteins. Some aspects of Mj0307's unique behavior can be explained by comparing structure-based sequence alignments with mesophilic bacterial and eukaryotic glutaredoxin and thioredoxin proteins. It is proposed that Mj0307, and similar archaebacterial proteins, may be most closely related to the mesophilic bacterial NrdH proteins. Together these proteins may form a unique subgroup within the family of protein disulfide oxidoreductases.
Subject(s)
Methanococcus/enzymology , NADH, NADPH Oxidoreductases/chemistry , Oxidoreductases , Amino Acid Sequence , Cloning, Molecular , Disulfides , Escherichia coli/chemistry , Glutaredoxins , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Sequence Data , Protein Structure, Secondary , Protein Structure, Tertiary , Proteins/chemistry , Sequence Homology, Amino Acid , Temperature , Thioredoxins/chemistryABSTRACT
The geminate ligand recombination reactions of photolyzed carbonmonoxyhemoglobin were studied in a nanosecond double-excitation-pulse time-resolved absorption experiment. The second laser pulse, delayed by intervals as long as 400 ns after the first, provided a measure of the geminate kinetics by rephotolyzing ligands that have recombined during the delay time. The peak-to-trough magnitude of the Soret band photolysis difference spectrum measured as a function of the delay between excitation pulses showed that the room temperature kinetics of geminate recombination in adult human hemoglobin are best described by two exponential processes, with lifetimes of 36 and 162 ns. The relative amounts of bimolecular recombination to T- and R-state hemoglobins and the temperature dependence of the submicrosecond kinetics between 283 and 323 K are also consistent with biexponential kinetics for geminate recombination. These results are discussed in terms of two models: geminate recombination kinetics modulated by concurrent protein relaxation and heterogeneous kinetics arising from alpha and beta chain differences.
