Polypeptides extinction coefficient

Second, for studying the interaction of a non-glycosylated protein with a glycoprotein, such as the example presented in section IIIB, we still can use Eq. [5]. In order to use this equation, we must be able to calculate the polypeptide extinction coefficient of the complex,The p of a complex with a known stoichiometry (AfpBn) can be calculated using the following equation ... 

The internal structure of the cross-linked synthetic polypeptides is maintained by heat-stable, covalent bonding between the cross-linked amino acid side chains and by heat-labile, noncovalent side chain interactions between glutamic acid and lysine residues (electrostatic) and between tyrosine residues (nonpolar). The stability of the spatial structure of a polymer depends upon the relative proportion of covalent and noncovalent bonding that it contains and increases as the number of cross-links increases. According to the current theories of protein structure, the charged amino acid residues would be arrayed on the surface of the molecule, and the tyrosine residues would be internally placed and thus interact to give a hypochromic effect. Am(6)-poly Glu52Lys33Tyr15 (No. 3B) (Fr. 1) displays such an effect, and the molar extinction coefficient of the cross-linked derivative is 25% lower than that of the parent polymer. This hypo-... 

The phycobiliproteins are hard to beat as extremely bright antibody labels for fluorescence analysis of cell surface antigens by flow cytome-try 15,16 These bacterial photosynthetic macromolecules each have up to 34 individual bilin fluorophores wrapped within the polypeptide structure. An example is R-phycoerythrin (R-PE), which has an extinction coefficient of 2 X 10 L/mol cm and a quantum yield of 0.68. Usually there is room for only one PE molecule per antibody, because the size of an R-PE label is 1.5 times that of an IgG antibody. The large size of the complex reduces the kinetics of binding to cell surface antigens, and some intracellular markers are inaccessible to the R-PE-labeled antibody. For intracellular measurements, lower molecular mass fluorophores (<1 kDa) are usually preferred. 

Photosystem I (PS I) reaction center complex consists of two large subunits which carry antenna chlorophyll P-700 and early electron acceptors and several small subunits, one of which contains the iron-sulfur centers, F and Fg. Because the PS I complexes are usually isolated with detergents, careful evaluation of detergent-effects, such as solubilization of chlorophyll a, or inactivation of P-700, is essential for determination of stoichiometry of subunit polypeptides and functional constituents in the complex. Recently, we have shown that the differential extinction coefficient of P-700 is markedly affected by sodium dodecyl sulfate (SDS) which induces a band-shift of chlorophyll molecules at 690 nm [1]. Herein, we report effects of other detergents on the extinction coefficient of P-700 and provide a simple method to estimate the extinction coefficient in PS I preparations treated with various detergents. Using the extinction values thus determined,... 

The reduced-minus-oxidized differential extinction coefficient of P-700 at the peak wavelength of the 700 nm band was determined by measuring oxidation of TMPD coupled with reduction of flash-oxidized P-700 according to the method of Hiyama and Ke [1,6]. Polypeptide compositions of PS I complexes were analyzed by SDS polyacrylamide gel... 

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