Enzymatic conjugation

The metabolic formation of N-sulfonyloxy-N-acetyl-2-aminofluorene (N-sulfonyloxy-AAF) and its observed electrophilic reactivity, provided the first evidence for the importance of enzymatic conjugation reactions in chemical carcinogenesis (23,24). This reaction was shown to be catalyzed by PAPS-dependent sulfotrans-ferases that are located predominantly in liver cytosol and has been subsequently demonstrated for N-hydroxy arylamide metabolites of several other carcinogens, including N-acetyl-4-aminobiphenyl (AABP), benzidine, N-acetyl-2-aminophenanthrene and phenacetin. 

Dekant W, Vamvakas S, Henschler D, et al. 1988b. Enzymatic conjugation of hexachloro-1,3-butadiene with gultathione. Formation of 1 -(Glutathion-S-yl)-l, 2,3,4,4-pentachlorobuta-1,3-diene and 1,4-... 

The purposes of this paper are to review one of the common mechanisms of detoxication in plants, namely conjugation, and to present data showing that salicylic acid, an allelopathlc phenolic acid, is enzymatically conjugated by oat roots. 

Methyl iodide incubated with human erythrocytes conjugates nonenzymatically with glutathione. In addition, an enzymatic conjugation was apparent with erythrocytes from 10/17 donors, but even among these people, the nonenzymatic process was dominant (Hallier et al., 1990). 

The absorbance measurement conducted in these assays can be replaced by fluorescence detection (fluorescence ELISA). In this case, the enzymatic conjugate chosen is an alkaline phosphatase that converts the specific substrate into a fluorescent compound. 

Mainigi and Campbell (20) have shown that low protein diets depress hepatic glutathione levels. Since enzymatic conjugation and spontaneous reaction of certain xenobiotics with hepatic glutathione is an important detoxication step with certain compounds, this depression of glutathione levels may alter the toxicity of these compounds in animals fed low protein diets. 

Peters noted in a recent review [52] that only a few works published have used simple dilution for the preparation of urine samples. The dilution factors ranged from 5- to 50-fold. Eichhorst et al. also used (tenfold) dilution in their procedure, but only after urine samples had been submitted to enzymatic conjugate cleavage [120],... 

Yang, R.S.H., Enzymatic conjugation and insect metabolism, In Insecticide biochemistry and physiology, Wilkinson, C.F., Ed., New York Plenum Press, 1976, p. 177. 

A new translation. A transfer RNA with a UGU anticodon is enzymatically conjugated to i C-labeled cysteine. The cysteine unit is then chemically modified to alanine (with the use of Raney nickel, which removes the sulfur atom of cysteine). The altered aminoacyl-tRNA is added to a protein-synthesizing system containing normal components except for this tRNA. The mRNA added to this mixture contains the following sequence ... 

The ubiquitinylation of proteins is a complex process, which involves three sequential enzymatic reactions performed by three types of enzymes, El, E2 and E3 (Fig. 2.9). The enzymatic conjugating cascade is organized in a hierarchical way There is one El enzyme, a limited number of E2 enzymes, each of which may serve several E3 enzymes, and a much larger number of E3 enzymes (Fig. 2.10). 

Robertson, 1. G. C, and JemstrSm, B., The enzymatic conjugation of glutathione with bay-region diol-epoxides of benzo(a)pyFene, benz(a)anthracene and chrysene. Carcinogenesis (London) 7, 1633-1636 (1986). 

Phase II biotransformation involves the enzymatic conjugation of a polar molecule to the drug molecule or to the phase I metabolite. These reactions include glucuronidation, acetylation, sulfation, or amidation. 

The enzymatic conjugation using rat liver cytosol produces a mixture of the 4- and 5-thioether conjugates. However, the diastereoisomers of the conjugates are not formed in equal amounts. With a purified enzyme from the Little River Skate, an equal mixture of the 4- and 5-thioether conjugates are produced. But in this case, only one of the diastereoisomers of each positional isomer is produced. Product analysis of the SH conjugates obtained from C-labeled BP-4,5-oxide (4,5- C) established some definite stereochemical requirements for the catalytic step (12). 

Hernandez, 0., M. Walker, R. Cox, G.L. Foureman, B. Smith, and J.R. Bend, Regioselectivity and Stereospecificity in the Enzymatic Conjugation of Glutathione with (+) Benzo(a)pyrene... 

Protein Fusion to AfQnity Ligands and Enzymatic Conjugation.965... 

Protein Fusion to Affinity Ligands and Enzymatic Conjugation... 

FIGURE 44.6 (a) Enzyme immobilization to solid matrices via protein fusion to an affinity ligand and (b) enzymatic conjugation catalyzed by transglutaminase. 

Glucose oxidase Proteins Enzymatic conjugation Biosensor [69]... 

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