Enzyme transferring

FIGURE 23.15 The reactions of glycogen debranching enzyme. Transfer of a group of three o -(l 4)-linked glucose residues from a limit branch to another branch is followed by cleavage of the o -(l 6) bond of the residue... 

The isomerase (EC 5.3.3.1) from Pseudomonas testosteroni has been studied in detail. This enzyme transfers a hydrogen from position 4 to the 6fl-position. Although several isomerases have been detected, their presence is often seen as presenting problems as they frequently lead to product diversification. 

Enzymes transferring an acetyl moiety to one specific of several amino-groups of the aminocyclitol-aminoglycoside antibiotics (e.g. gentamicin, amikacin, kanamycin) are called aminoglycoside acetyltransferases... 

As we have noted, the outcome of a virus infection is the synthesis of viral nucleic acid and viral protein coats. In effect, the virus takes over the biosynthetic machinery of the host and uses it for its own synthesis. A few enzymes needed for virus replication may be present in the virus particle and may be introduced into the cell during the infection process, but the host supplies everything else energy-generating system, ribosomes, amino-acid activating enzymes, transfer RNA (with a few exceptions), and all soluble factors. The virus genome codes for all new proteins. Such proteins would include the coat protein subunits (of which there are generally more than one kind) plus any new virus-specific enzymes. 

Deuterium substitution for the migrating 4/ proton demonstrates that the enzyme transfers it by a stereospecific intramolecular path... 

In the classical procedures W, the 5-T or D-labeled mevalonate is converted enzymatically to farnesol, which is then oxidized to famesal by liver alcohol dehydrogenase. This enzyme transfers the pro-R hydrogen of C—1 of ethanol or geraniol (or farnesol) to the 4 pro R position of the nicotinamide ring of NAD. 

Both muscle and liver have aminotransferases, which, unlike deaminases, do not release the amino groups as free ammonium ion. This class of enzymes transfers the amino group from one carbon skeleton (an amino acid) to another (usually a-ketoglutarate, a citric acid cycle intermediate). Pyridoxal phosphate (PLP) derived from vitamin is required to mediate the transfer. 

This enzyme [EC 2.4.1.56] catalyzes the reaction of UDP-A-acetyl-D-glucosamine with a lipopolysaccharide to produce UDP and an A-acetyl-D-glucosaminyl-lipopoly-saccharide. Thus, this enzyme transfers A-acetylgluco-saminyl residues to a D-galactose residue in the partially completed lipopolysaccharide core. 

A major class of enzymes that catalyze the transfer of a group or moiety from one compound to another. The groups being transferred can be one-carbon units such as methyl, hydroxyhnethyl, carbamoyl, or amidino moieties. Enzymes transferring aldehyde or ketonic groups such as transketolase are members of this class. Other examples include acyltransferases, glycosyltransferases, aminotransferases, phosphotransferases, and sulfotrans-ferases. 

F3. Fevery, J., Leroy, P., and Heirwegh, K. P. M., Enzymic transfer of glucose and xylose from uridine diphosphate xylose to bilirubin by untreated and digitonin-activated preparations from rat liver. Biochem. J. 129, 619-633 (1972). 

Chapter 2 summarizes the application of transferases in polymer chemistry. Transferases are enzymes transferring a group from one compound (donor) to another compound (acceptor). Of the three classes of enzymes used in polymer science, transferases are the least frequently applied, which is due to their sensitivity. Nonetheless, several transferases such as phosphorylases and synthases have been... 

Enzymic transfer of D-xylose from uridine 5 -(D-xylopyranosyI-HC pyrophosphate) to L-serine residues of endogenous protein acceptors from (a) a cell tumor of the mouse188 and (b) chick-embryo cartilage189 occurs in cell-free extracts of both of these tissues, in the absence of biosynthesis of protein. The enzyme preparations employed were from the supernatant liquor, although activity was also present in the insoluble fractions. In these two types of tissue, the acceptors are heparin and chondroitin sulfate, respectively, but the presence of other D-xylose-containing glycoproteins in ascites fluid from... 

The cytochromes P-450 monooxygenase system is actually a collection of isoenzymes, all of which possess an iron protoporphyrin IX as the prosthetic group. The monomer of the enzyme has a molecular weight of 45,000 to 55,000. The enzyme is membrane bound within the endoplasmic reticulum. Cytochromes P-450 are closely associated with another vital component of the system, NADPH cytochrome P-450 reductase. This is a flavoprotein, which has 1 mol of FAD and 1 mol of FMN per mol of apoprotein. The monomeric molecular weight of the enzyme is 78,000. The enzyme transfers two electrons to cytochromes P-450, but one at a time. There only seems to be one reductase, which serves a group of isoenzymes of cytochromes P-450, and consequently, its concentration is 1/10 to 1/30 that of cytochromes P-450. 

The genetic basis for the ABO blood groups is well understood. There are three alleles, variants of a gene, that encodes a glycosyltransferase. In A type individuals, this enzyme transfers N-acetyl-galactosamine from a carrier molecule, called UDP... 

When 31P is bonded to lsO the chemical shift of the 31P is altered by 0.0206 ppm from that when the phosphorus is bonded to leO. This allows lsO labels introduced into phospho groups to serve as tracers which can be followed continuously during reactions.683 The technique is useful in studies of stereochemistry (see Section 2) and for examination of positional isotope exchange.690 This latter technique is often used with ATP containing lsO in the P,y-bridge position. If an enzyme transfers the terminal (y) phospho group to an acceptor via a phosphoenzyme but without loss of the ADP, we may expect positional isomerization. The lsO will move between the P,y-bridge position and... 

Tire enzyme does not require lipoic acid. It seems likely that a thiamin-bound enamine is oxidized by an iron-sulfide center in the oxidoreductase to 2-acetyl-thiamin which then reacts with CoA. A free radical intermediate has been detected318 321 and the proposed sequence for oxidation of the enamine intermediate is that in Eq. 15-34 but with the Fe-S center as the electron acceptor. Like pyruvate oxidase, this enzyme transfers the acetyl group from acetylthiamin to coenzyme A. Cleavage of the resulting acetyl-CoA is used to generate ATR An indolepyruvate ferredoxin oxidoreductase has similar properties 322... 

Several selenoproteins have been found in certain bacteria and archaea. A hydrogenase from Methano-coccus vannielii contains selenocysteine.559 560 This enzyme transfers electrons from H2 to the C-5 si face of the 8-hydroxy-5-deazaflavin cofactor F q (Section B,4). The same bacterium synthesizes two formate dehydrogenases (see Fig 15-23), one of which contains Se. Two Se-containing formate dehydrogenases are made by E. coli. One of them, which is coupled to a hydrogenase in the formate hydrogen-lyase system (see Eq. 15-37), is a 715-residue protein containing selenocysteine at position 140.561-563 The second has selenocysteine at position 196 and functions with a nitrate reductase in anaerobic nitrate respiration.561... 

There are still other important factors. Occupancy of the receptor by a ligand makes the receptor protein itself a substrate for the chemotaxis-specific methyl-transferase encoded by the cheR gene.62 70 71 This enzyme transfers methyl groups from S-adenosyl-methionine to specific glutamate side chains of the receptor to form methyl esters. In the aspartate receptor there are four such glutamate residues in a large cytoplasmic domain that includes the C terminus. 

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