Protein Folding Chaperoned and Unchaperoned

A commonly employed convention is to characterize the molecular mass of the protein by using the lightest isotopes. This is reasonable because for lighter atoms, such as C, H, O, N, S, and P, the stable isotopes of lowest atomic mass are also the most abundant isotopes. For the 69-amino acid protein of formula C398H8,8N,ooO,32S3, the lowest molecular mass is derived from the combined masses of the lightest nuclides of each element and equals 9,006.4 or 9,006 Da (9.006 KDa). This species is calculated to account for only 0.5 percent of the distribution noted above. Experimentally, it becomes an issue of sensitivity to accurately determine the first (lowest mass) peak in the series of istopic peaks the lowest monoisotopic molecular mass. 

In 1993, Stephen B. H. Kent (1945- ) and collaborators used automated peptide synthesis to construct all-D-amino acid superoxide dis-mutase. As expected it folded so as to be the mirror image of the native (all-L) enzyme. This D-protein is equally effective as the native protein in catalyzing the disappearance of superoxide (O2 ), a toxic species, because superoxide is achiral. The potential advantage of this approach is that D-proteins should not be destroyed by natural proteases nor should they ehcit immune responses. 

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