Prosthetic groups secondary structure

Each protein in a sample is unique and can demonstrate that individuality in protein assays as variation in the color response. Such protein-to-protein variation refers to differences in the amount of color (absorbance) that are obtained when the same mass (microgram or milligram) of various proteins are assayed concurrently (i.e., in the same run) by the same method. These differences in color response relate to differences among proteins due to amino acid sequence, isoelectric point (pi), secondary structure, and the presence of certain side chains or prosthetic groups. 

Circular dichroism (CD) spectroscopy is a sensitive analytical tool for assessing protein structure. It can detect changes in both the secondary and tertiary structure of proteins, as well as provide information regarding prosthetic groups, bound ligands and co-factors. The origin of circular dichroism in proteins is described and various applications of CD spectroscopy to the study of protein structure, function, and folding is discussed. 

The crystal structure of canine MPO has recently been determined to 3-A resolution (7, 14). This mammalian enzyme is a covalently linked dimer of molecular weight 140 kDa that can be cleaved into two identical halves by reduction of a single disulfide bond. Each half of the dimer, termed hemi-MPO, has the same optical properties and catalytic activity as the parent. Hemi-MPO consists of two polypeptides of 466 and 108 amino acid residues, and a heme-type prosthetic group is covalently bound to the larger polypeptide in a crevice 15 A below the protein surface. Like CCP and LIP, the secondary structure of MPO is dominated by a-helices with relatively little /3-sheet structure (Fig. 

MAO catalyzes the oxidative deamination of catecholamines, 5-hydroxytryptamine (serotonin), and other monoamines, both primary such as NE, and secondary such as EP. It is one of several oxidase-type enzymes whose coenzyme is the flavin-adenine-dinucleotide (FAD) covalently bound as a prosthetic group (Fig. 9-3). The isoalloxazine ring system is viewed as the catalytically functional component of the enzyme. In a narrow view N-5 and C-4a is where the redox reaction takes place (i.e., +H+, +le or -H+, -le), although the whole chromophoric N-5-C-4a-C-4-N-3-C-2-N-l region undoubtedly participates. Figure 9-3 is a proposed structure of MAO isolated from pig brain (Salach et al., 1976).4... 

The tertiary structure of a protein is the three-dimensional arrangement of all the atoms in the molecule. The conformations of the side chains and the positions of any prosthetic groups are parts of the tertiary structure, as is the arrangement of helical and pleated-sheet sections with respect to one another. In a hbrous protein, the overall shape of which is a long rod, the secondary structure also provides much of the information about the tertiary structure. The helical backbone of the protein does not fold back on itself, and the only... 

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