Relative coenzyme

Yet another difference is that laboratory reactions are often done using relatively small, simple reagents such as Br2, HC1, NaBH4, OO3, and so forth, while biological reactions usually involve relatively complex "reagents" called coenzymes. In the hexokinase-catalyzed phosphorylation of glucose just shown,... 

Divalent sulfur compounds are achiral, but trivalent sulfur compounds called sulfonium stilts (R3S+) can be chiral. Like phosphines, sulfonium salts undergo relatively slow inversion, so chiral sulfonium salts are configurationally stable and can be isolated. The best known example is the coenzyme 5-adenosylmethionine, the so-called biological methyl donor, which is involved in many metabolic pathways as a source of CH3 groups. (The S" in the name S-adenosylmethionine stands for sulfur and means that the adeno-syl group is attached to the sulfur atom of methionine.) The molecule has S stereochemistry at sulfur ana is configurationally stable for several days at room temperature. Jts R enantiomer is also known but has no biological activity. 

The application of magnetic resonance techniques to biological systems is a relatively new approach for the study of macromolecules. In this review we have presented the different approaches which have been made to study Bi2-enzymes. Clearly some progress has been made particularly from the application of ESR to a study of the enzymes ethanolamine ammonia-lyase and ribonucleotide reductase. Although 13C NMR is well in its developmental stages it is obvious that this technique will prove to be very useful for the examination of coenzyme-enzyme interactions. Studies of how corrinoids bind in enzymes and how sulfhydryl containing proteins are involved in enzyme catalysis comprise two major problems which must be overcome before realistic mechanisms can be presented for this group of enzymes. 

An enzyme consists of a polypeptide chain with a particular spatial configuration specific to that sequence of amino acids. The molecule twists and turns, forming structural features that are catalytically active, these being known as active sites. There may be more than one active site per enzyme molecule. Sometimes an auxiliary catalyst, known as a coenzyme, is also needed. Apparently, only the relevant active site of the enzyme comes into contact with the substrate and is directly involved in the catalysed reaction. The active site consists of only a few amino acid residues. These are not necessarily adjacent to one another in the peptide chain but may be brought into proximity by the characteristic folding of the enzyme structure. The active site may also include the coenzyme. The remainder of the enzyme molecule fulfils the essential function of holding the components of the active site in their appropriate relative positions and orientation. 

Intermediates of the metabolism have so far not been identified as inhibitors or activators of PHA synthases. The only exception is coenzyme A which inhibits the PHA synthases of R. eutropha, C. vinosum, and R aeruginosa at relatively low concentrations [73,74]. It is not known whether this inhibition is physiologically relevant. The inhibition by coenzyme A has, however, to be taken into account during the design of in vitro PHA biosynthesis processes, if PHA is being prepared on a preparative scale recycling of coenzyme is then recommended not only to reduce the costs but also to improve the kinetics of PHA formation. 

Malonyl-CoA Acyl carrier protein transacylase (MCAT or FabD) catalyzes the transfer of a malonyl group between coenzyme A and acyl carrier proteins that are the privileged transporters of the FASH system. Although essential, this enzyme is present in excess and does not have a regulatory role in the FASH pathway, which might explain the relative paucity of reported inhibitors [1],... 

Nutritional deficiency diseases are relatively rare in the temperate zone. The etiology of numerous other clinical conditions involve vitamin deficiencies, due to faults in absorption, transfer, or utilization. Because of the central position of the vitamins as sources of coenzymes, such functional deficiencies are important in malabsorption, where the picture is often complicated by multiple deficiencies, in anemias where the defect is in general highly specific, and in many other diseases where the deficiency is secondary to other pathologic events, but nevertheless of grave consequences. 

Many enzymes require the participation of dissociable coenzymes such as NAD+, NADP+ or ATP for their catalytic activities. The use of coenzymes to activate immobilized enzymes on a large scale is hampered by their relatively low stability and high cost. Attempts are therefore being made to stabilize the coenzymes and to find suitable means for their continuous regeneration. The principal approach has been to covalently attach a co-enzyme to a polymeric water-soluble matrix, thus making the co-enzyme, like the enzyme, potentially reusable (9,10). 

ATP and magnesium were required for the activation of acetate. Acetylations were inhibited by mercuric chloride suggesting an SH group was involved in the reaction either on the enzyme or, like lipoic acid, as a cofactor. Experiments from Lipmann s laboratory then demonstrated that a relatively heat-stable coenzyme was needed—a coenzyme for acetylation—coenzyme A (1945). The thiol-dependence appeared to be associated with the coenzyme. There was also a strong correlation between active coenzyme preparations and the presence in them of pantothenic acid—a widely distributed molecule which was a growth factor for some microorganisms and which, by 1942-1943, had been shown to be required for the oxidation of pyruvate. 

Folate, the anion of folic acid, is made up of three different components—a pteridine derivative, 4-aminobenzoate, and one or more glutamate residues. After reduction to tetrahydrofolate (THF), folate serves as a coenzyme in the Q metabolism (see p. 418). Folate deficiency is relatively common, and leads to disturbances in nucleotide biosynthesis and thus cell proliferation. As the precursors for blood cells divide particularly rapidly, disturbances of the blood picture can occur, with increased amounts of abnormal precursors for megalocytes megaloblastic anemia). Later, general damage ensues as phospholipid... 

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