We found that cyt c Y67H and Y67R variants represent a state which resembles the conformational intermediate state in cyt c with high peroxidase activity; and also the hydrogen bond network around Tyr67 is associated with the conformational transition of cyt c; these suggest that the hydrogen bond network around Tyr67 is essential in maintaining the cyt c functioning not only as an electron transfer protein but also probably as a trigger in apoptosis.
Conformational transitions in cytochrome c (cyt c) are being realized to be responsible for its multi-functions. Among a number of conformational transitions in cyt c, the alkaline transition has attracted much attention. The cDNA of human cyt c is cloned by RT-PCR and a high-effective expression system for human cyt c has been developed in this study. The equilibrium and kinetics of the alkaline transition of human cyt c have been systematically investigated for the first time, and compared with those of yeast and horse cyt c from an evolutionary perspective. The pK(a) value for the alkaline transition of human cyt c is apparently higher than that of yeast and horse. Kinetic studies suggest that it is increasingly difficult for the alkaline transition of cyt c from yeast, horse and human. Molecular modeling of human cyt c shows that the omega loop where the lysine residue is located apparently further away from heme in human cyt c than in yeast iso-1 and horse heart cyt c. These results regarding alkaline conformational transition provide valuable information for understanding the molecular basis for the biological multi-functions of cyt c.
The continued interest in protein engineering has led to intense efforts in developing novel stable enzymes, which could not only give boost to industrial and biomedical applications, but also enhance our understanding of the structure-function relationships of proteins. We present here the generation of three hybrid proteins of cytochrome c (cyt c) and peroxidase via structure-based rational mutagenesis of cyt c. Several residues (positions 67, 70, 71 and 80) in the distal heme region of cyt c were mutated to the highly conserved amino acids in the heme pocket of peroxidases. The multiple mutants were found to exhibit high peroxidase activity and conserve the impressive stability of cyt c. We expect that this strategy could be extended to other cases of metalloprotein engineering, and lead to the development of stable and active biocatalysts for industrial uses. Besides, this study also provides insight into the structure-function relationships of hemoproteins.
Let n n Hermitian matrix A have eigenvalues 1 ; 2 ; ; n , and let k k Hermitian matrix H have eigenvalues 1 2 k , and let Q be an n k matrix having full column rank, so 1 k n. It is proved that there exist k eigenvalues i1 i2 ik of A such that max 1jk j j , ij j c min Q kAQ , QHk 2 ;
Due to the awareness of fossil fuel depletion and global warming, biorefinery for production of biofuels and valuable platform chemicals from lignocellulosic biomass has attracted growing interest in the past decades. With the rising concept of comprehensive utilization of lignocellulosic biomass,fractionation processes are generally necessary prior to its subsequent conversion with aims to produce purified cellulose with specific recovery of hemicellulose and lignin. In this review, ionic liquids fractionation,steam explosion based fractionation,twin-screw extrusion and organosolv fractionation are described and their features and comparative performances are discussed.
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