Proteins occurrence

B12. Bennett, R. M., Cornell, K. A., Merritt, M. J., Bakke, A. C., Hsu, P. H., and Hefeneider, S. H., Autoimmunity to a 28—30 kD cell membrane DNA binding protein Occurrence in selected sera from patients with SLE and mixed connective tissue disease (MCTD). Clin. Exp. Immunol. 86, 374-379 (1991). 

The VFe protein also has the equivalent of P-cluster pairs which have similar properties to those found in the MoFe protein (159). No information is available on whether P-cluster pairs exist in the FeFe protein, but because of the relatively high sequence identity and the similar genetic basis of its biosynthesis, the occurrence seems highly likely. The catalytic role assigned to the P-cluster pair involves accepting electrons from the Fe protein for storage and future deUvery to the substrate via the FeMo-cofactor centers. As of this writing (ca early 1995), this role has yet to be proved. 

Amino acids essential for young rats (98) and fishes (99) have been reviewed. Rats preferably eat a diet with sufficient amounts of essential amino acids rather than one that is deficient (100). Each essential amino acid, consumed in self-selection, has been reviewed (101). A protein diet with an excess of essential amino acids has been described as a poor protein diet from investigations that showed remarkable growth inhibition and occurrence of fatty fiver disease in rats (102). This is called amino acid imbalance (103). 

Amino acid Three- letter code One- letter code Mass of residue in. b proteins Accessible surface area, 2 nm Hydrophobicity index ionizable side chain Occurrence in n/ proteins, /o Relative mutabihty... 

Based on the frequency of occurrence for each residue in the sequence of 207 unrelated proteins (8). 

Frequency of Occurrence of Amino Acid Residues in Proteins... 

Frequency of occurrence of each amino acid re.sidue in the polypeptide chain.s of 207 unrelated protein.s of known. sequence. 

The tendencies of the amino acids to stabilize or destabilize a-helices are different in typical proteins than in polyamino acids. The occurrence of the common amino acids in helices is summarized in Table 6.1. Notably, proline (and hydroxyproline) act as helix breakers due to their unique structure, which fixes the value of the —N—C bond angle. Helices can be formed from either... 

FIGURE 6.39 Relative frequencies of occurrence of amino acid residues in m-helices, /3-sheets, and /S-turns in proteins of known structure. (Adapted from Belt, J E., and Belt, E. T, 1988, Proteins and. Enzymes, Englewood Cliffs, NJ Prentice-Hall.)... 

Thus, based on material applications, the following polymers are important natural rubber, coal, asphaltenes (bitumens), cellulose, chitin, starch, lignin, humus, shellac, amber, and certain proteins. Figure 4 shows the primary structures of some of the above polymers. For detailed information on their occurrence, conventional utilization, etc., refer to the references cited previously. 

Energy transfer to fluorescent proteins. There are marked differences among the various bacterial species and strains in terms of the in vivo luminescence spectra. The emission maxima are spread mostly in a range from 472 to 505 nm (Seliger and Morton, 1968), but one of the strains, P. fischeri Y-l, shows a maximum at 545 nm (Ruby and Nealson, 1977), as shown in Fig. 2.3. However, the in vitro luminescence spectra measured with purified luciferases obtained from the various bacterial species and strains are all similar (Amax about 490 nm). The variation in the in vivo luminescence spectra may be due to the occurrence of an intermolecular energy transfer that increases the efficiency of light emission. 

Isolated chitins are highly ordered copolymers of 2-acetamido-2-deoxy-/3-D-glucose and 2-amino-2-deoxy-j6-D-glucose. The occurrence of the latter is explained by the fact that in vivo chitin is covalently finked to proteins via the nitrogen atom of approximately one repeating unit out of ten, therefore upon isolation a degree of deacetylation close to 0.10 is found. Chito-biose, 0-(2-amino-2-deoxy-j6-D-glucopyranosyl)-(l 4)-2-amino-2-deoxy-... 

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