Mobile carboxyl carrier

Neither catalytic component contains a trace of bound biotin. The biotin prosthetic group is covalently linked to the third component, carboxyl carrier protein (CCP—biotin). As with other biotin enzymes, the bicyclic ring of the prosthetic group resides at the distal end of a flexible 14 A side chain which allows it to act as a mobile carboxyl carrier between the two catalytic centers as illustrated below. A large number of biotin-dependent enzymes which carry out diverse reaction types are now known. All of these reactions proceed through a carboxylated intermediate with the carboxybiotinyl prosthetic group functioning as a mobile carboxyl carrier . 

These biochemical transformations occur on a multienzyme complex composed of at least three dissimilar proteins biotin carrier protein (MW = 22,000), biotin carboxylase (MW = 100,000) and biotin transferase (MW = 90,000). Each partial reaction is specifically catalyzed at a separate subsite and the biotin is covalently attached to the carrier protein through an amide linkage to a lysyl a-amino group of the carrier protein (338, 339). In 1971, J. Moss and M. D. Lane, from Johns Hopkins University proposed a model for acetyl-CoA carboxylase of E, coli where the essential role of biotin in catalysis is to transfer the fixed CO2, or carboxyl, back and forth between two subsites. Consequently, reactions catalyzed by a biotin-dependent carboxylase proceed though a carboxylated enzyme complex intermediate in which the covalently bound biotinyl prosthetic poup acts as a mobile carboxyl carrier between remote catalytic sites (Fig. 7.13). 

Among anticoccidials, polyether antibiotics have been the most widely used in the broiler industry over the last two decades because they provide excellent disease control and are refractory to resistance development (3). Polyether antibiotics are branch chained, polyoxygenated carboxylic acids that act as mobile carriers of cations (4) by rendering cations lipid-soluble, thereby enabling them to pass across membranes. This process disrupts cationic cross-membrane gradients and is responsible for their anticoccidial activity T3J. 

The complex is a mobile carrier of carboxyl groups according to the following general scheme ... 

Ionic Additives. Cotransport of anions is the most obvious way to maintain electroneutrality, but alternative means have been explored. In recent years, many studies have been conducted which examine the use of anionic membrane additives for maintenance of electroneutrality (35, 54-58), The anionic additives can be either stationary or mobile and are typically lipophilic carboxylic, phosphoric, or sulfonic acids. Neutral macrocyclic carriers coupled with anionic additives result in a synergistic transport of cations which exceeds that accomplished by each component individually. 

Alternative p-Type Semiconductors Because the valence band potential of NiO lies only 100 mV more positive than the optimum redox couple for n-type devices, a substantial increase in voltage for the p-type/tandem systems should be achieved if the p-type semiconductor has a valence band with a much lower energy than the triiodide/iodide redox couple. The other requirements for the material include optical transparency (Eg > 3 eV), mechanical and electrochemical stability, good electronic properties (high charge-carrier mobility) and a convenient means of anchoring the dye (e.g. metal oxides and carboxylic acids). Whilst other p-type semiconductors exist, few combine all the properties required and as yet there have been no p-type semiconductors reported that perform better than NiO in a p-type For example, several... 

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