Prosthetic groups conjugated

Conjugated proteins Proteins with a prosthetic group ... 

Casein may be considered to be a conjugated protein, that is the protein is associated in nature with certain non-protein matter known as prosthetic groups. In the case of casein the prosthetic group is phosphoric acid. The protein molecule is also associated in some way with calcium. The presence of these inorganic materials has an important bearing on the processability and subsequent use of casein polymers. 

FIGURE 25.6 Fatty acids are conjugated both to coenzyme A and to acyl carrier protein through the sulfliydryl of phosphopantetheine prosthetic groups. 

The spectral properties of four major phycobiliproteins used as fluorescent labels can be found in Tables 9.1 and 9.2. The bilin content of these proteins ranges from a low of four prosthetic groups in C-phycocyanin to the 34 groups of B- and R-phycoerythrin. Phycoerythrin derivatives, therefore, can be used to create the most intensely fluorescent probes possible using these proteins. The fluorescent yield of the most luminescent phycobiliprotein molecule is equivalent to about 30 fluoresceins or 100 rhodamine molecules. Streptavidin-phycoerythrin conjugates, for example, have been used to detect as little as 100 biotinylated antibodies bound to receptor proteins per cell (Zola et al., 1990). 

HRP is a hemoprotein containing photohemin IX as its prosthetic group. The presence of the heme structure gives the enzyme its characteristic color and maximal absorptivity at 403 nm.The ratio of its absorbance in solution at 403 nm to its absorbance at 275 nm, called the RZ or Reinheitzahl ratio, can be used to approximate the purity of the enzyme. However, at least seven isoenzymes exist for HRP (Shannon et al., 1966 Kay et al., 1967 Strickland et al., 1968), and their RZ values vary from 2.50 to 4.19. Thus, unless the RZ ratio is precisely known or determined for the particular isoenzyme of HRP utilized in the preparation of an antibody-enzyme conjugate, subsequent measurement after crosslinking would yield questionable results in the determination of the amount of HRP present in the conjugate. 

An apoenzyme is the part of a conjugated en2yme without the prosthetic group. 

Many enzymes require additional substances in order to function effectively. Conjugated enzymes require a prosthetic group before they are catalytically active, such groups being covalently or ionically linked to the protein molecule and remaining unaltered at the end of the reaction. Catalase (EC 1.11.1.6), for instance, contains a haem group while ascorbate oxidase (EC 1.10.3.3) contains a copper atom. 

Conjugated proteins consist of a protein part (apoprotein) and a nonprotein part (prosthetic group). 

Figure S.A4. shows the structure of haemoglobin, a conjugate protein where there are extensive regions of a helix around the prosthetic group which is an iron porphyrin.

These BCAs chelate metal atoms by holding them in the center of their nitrogenous ring structure, in a manner similar to the chelation of iron at the core of a porphyrin prosthetic group. The excellent stability of this complex allows the use of DOTA, NOTA, and TETA conjugates in vivo with minimal potential for leaching and deleterious side effects. 

Phase II Reactions. As with phase I reactions, phase II reactions usually depend on several enzymes with different cofactors and different prosthetic groups and, frequently, different endogenous cosubstrates. All of these many components can depend on nutritional requirements, including vitamins, minerals, amino acids, and others. Mercapturic acid formation can be cited to illustrate the principles involved. The formation of mercapturic acids starts with the formation of glutathione conjugates, reactions catalyzed by the glutathione -transferases. 

The nonprotein part of a conjugated protein. Examples of prosthetic groups are sugars, lipids, nucleic acids, and metal complexes, (p. 1190)... 

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