Polypeptide chain molecular weight

Polypeptide Chain Molecular Weight Determination by Gel Permeation Studies on Agarose Columns in 6M Guanidinium Chloride... 

K.G. Mann and W.W. Fish, Protein polypeptide chain molecular weights by gel chromatography in guanidinium chloride, in C.H.W. Hirs and S.N. Timasheff (Eds.), Methods in Enzymology, Vol. XXVI, Enzyme Structure, Part C, Academic Press, New York, 1972, pp. 28-42. 

UQ may also be reduced by complex II (succinate ubiquinone oxido-reductase, succinate dehydrogenase), which contains four polypeptide chains, molecular weights 70,000, 27,000, 15,500, and 13,500. The first two constitute bona fide succinate dehydrogenase, a Krebs cycle enzyme catalyzing reaction... 

The transferrins are glycoproteins (i.e. compounds of proteins and carbohydrates) and include serum transferrin, lactoferrin (present in milk) and ovotransferrin (present in egg white). In humans, serum transferrin transports 40 mg of iron per day to the bone marrow. It contains a single polypeptide chain (molecular weight of 80000) coiled in such a way as... 

The basic structure of an immunoglobulin molecule, such as the major serum antibody IgG, consists of four polypeptide chains two identical light chains (molecular weight around 25 000 daltons) and two identical heavy chains (with a molecular weight around 50 000 daltons), cross-linked by disulfide bonds to form Y-shaped molecules with two flexible arms (Fig. 11.2). The binding sites are located on the arms and vary from one molecule to another (variable region) [22b]. 

Proteins are large polypeptides with molecular weights ranging from a few thousand into the millions. They contain 16% N on the average. Because some 20 amino acids are present in most proteins and there is no limitation to the size and amount of each amino acid a protein may contain, the number and types of proteins found in nature are almost limitless. Each protein has certain physical and chemical properties that are uniquely suited to its role in the living organism. The properties a protein may exhibit are ultimately a result of its amino acid content. Amino acid side chains determine whether the protein is water soluble, whether it is acidic or basic, and the shape it assumes. It is thus extremely important to study the amino acid content and sequences in proteins, as well as to ascertain their shapes and sizes. To exhibit a specific biologic property, a protein must not only contain the correct amino acid sequence but it must also have the appropriate size and shape. 

The first double bond inserted in an acyl chain is usually A9. The stearoyl-CoA A9 desaturase has been purified from rat liver (Strittmatter etal, 1974). This purification is extremely difficult because of the membranous and unstable nature of the desaturase. The terminal desaturase was found to be a single polypeptide of molecular weight 53 000 containing one atom of non-haem iron. Desaturase activity required NADH, stearoyl-CoA, oxygen, lipid and three proteins, cytochrome bs reductase, cytochrome bs and the desaturase. The cytochrome was the direct electron donor to the desaturase, which appeared (from EPR (electron paramagnetic resonance) studies) to utilize the iron in the oxidation/reduction sequence during desaturation of the fatty acyl substrate (Strittmatter et al, 1974). 

The a helix conformation of the polypeptide chains is demonstrated by three techniques infrared spectroscopy, circular dichroism and X ray diffraction. Infrared spectra exhibit the two characteristic bands of the a helix the amide I band at 1655 cm and the amide II band at 1545 cm . Circular dichroism spectra exhibit the two negative peaks characteristic of the a helix a broad peak centered at 222 nm and a peak at 209 nm. Low angle X ray patterns provide the parameter D of the hexagonal array of the polypeptide chains from D and the molecular chracteristics of the polypeptide, block (molecular weight m of the monomer unit and specific volume Vb of the polypeptide block) one obtains the length of the projection on the helix axis of the distance between two monomer units h = 2mVg (/3 N D ) with N = Avogadro s number the value found h = 1.50 0.02 A is the characteristic value of the a helix. 

Factor XIII. Factor XIII circulates in the blood as a zymogen composed of two pairs of different polypeptide chains designated A and B. Inert Factor XIII has a molecular weight of 350,000 daltons and is converted to its active transglutaminase form in the presence of thrombin and calcium. Activated Factor XIII, Xllla, induces an irreversible amide exchange reaction between the y-glutamine and S-lysine side chains of adjacent fibrin... 

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