Glutamate side chains

Figure 2 A glutamate side chain partitioned into quantum and classical regions. The terminal CH2C02 group IS treated quantum mechanically, and the backbone atoms are treated with the molecular mechanics force field.

Yet another cytotoxic agent that lacks the glutamate side chain illustrates the breadth of the SAR in this series. It is of note that the three nitrogen atoms in the fused six-membered ring system are disposed so as to form a pyridopyrazine rather than a pyrimidopyrimidine, as in piritrexim. The observation that this agent also inhibits tubulin may play an additional role in its activity. Nucleophylic aromatic... 

Carboxyl groups of certain glutamate side chains in proteins that control bacterial chemotaxis are methylated reversibly to form methyl esters.130 This carboxylmethylation occurs as part of a reaction sequence by which the bacteria sense compounds that can serve as food or that indicate the presence of food... 

In both carboxypeptidase A and thermolysin the active site Zn2+ is chelated by two imidazole groups and a glutamate side chain (Fig. 12-16). In carboxypeptidase A, Arg 145, Tyr 248, and perhaps Arg 127 form hydrogen bonds to the substrate. A water molecule is also bound to the Zn2+ ion. The presence of the positively charged side chain of Arg 145 and of a hydro-phobic pocket accounts for the preference of the enzyme for C-terminal amino acids with bulky, nonpolar side chains. The Zn2+ in thermolysin is also bound to two imidazole groups and that in D-alanyl-D-alanyl carboxypeptidase to three. 

A closely related E. coli protein is a 79-kDa multifunctional enzyme that catalyzes four different reactions of fatty acid oxidation (Chapter 17). The amino-terminal region contains the enoyl hydratase activity.32 A quite different enzyme catalyzes dehydration of thioesters of (3-hydroxyacids such as 3-hydroxydecanoyl-acyl carrier protein (see Eq. 21-2) to both form and isomerize enoyl-ACP derivatives during synthesis of unsaturated fatty acids by E. coli. Again, a glutamate side chain is the catalytic base but an imidazole group of histidine has also been implicated.33 This enzyme is inhibited irreversibly by the N-acetylcysteamine thioester of 3-decynoic acids (Eq. 13-8). This was one of the first enzyme-activated inhibitors to be studied.34... 

Closely related to aldolases is transaldolase, an important enzyme in the pentose phosphate pathways of sugar metabolism and in photosynthesis. The mechanism of the transaldolase reaction (Eq. 17-15) is similar to that used by fructose-1,6-bisphosphate aldolase with a lysine side chain forming a Schiff base and catalytic aspartate and glutamate side chains.198... 

All are probably bound to the microsomal membranes.503 507a An NADPH-dependent reductase reduces vitamin K quinone to its hydroquinone form. Conversion of Glu residues to Gla residues requires this reduced vitamin K as well as 02 and C02. During the carboxy-lation reaction the reduced vitamin K is converted into vitamin K 2,3-epoxide (Eq. 15-55).508 The mechanism is uncertain but a peroxide intermediate such as that shown in Eq. 15-56 is probably involved. This could be used to generate a hydroxide ion adjacent to the pro-S -H of the glutamate side chain of the substrate. This hydrogen could be abstracted by the OH to form... 

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. 

The synthesis of analogues of FA and MTX in which a nitrogen atom has been interposed between the benzene ring and the glutamate side-chain has been reported Scheme 3.128) [254,255]. Treatment of 2,10-diacetylpteroic... 

Since pH 7.5 is above the isoelectric point of hemoglobin A, the protein carries a negative charge and will migrate to the anode. At pH 7.5 the glutamate side chain has a negative charge, while valine... 

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