Synthase stereochemical course

Scheme XV. Stereochemical course of reactions catalyzed by tryptophan synthase.

FIGURE 14.15 (cont d). (c) Deduced stereochemical course of the reaction catalyzed by the enzyme citrate synthase. 

Scheme 4,18 Effect of the different stabilities of fluorothioester enolates (c/s effect) on the stereochemical course of the citrate synthase reaction on fluoroacetyl-CoA [36], In the active site of the enzyme, the enolate is assumed to be bound as the more stable E isomer, with the most electronegative substituents in their relative cis configuration.

The dehydration was shown to follow a j-jw-stereochemical course. The mechanism and specificity of various members of the enolase superfamily including OSB synthase have been reviewed and should be consulted for further details of the reaction mechanism. ... 

In order to determine the stereochemical course at during the normal replacement reaction, Chang and Walsh converted (Z)-DL-[4- H)vinylglycine and ( )-DL-[3,4- H2]vinylglycine to cystathionine in presence of cystathionine y-synthase Salmonella) and cysteine 280). Stereospecific chemical and enzymic degradation of the resultant samples of cystathionine to homoserine followed by comparison of the NMR spectra with those of authentic (4/ )- and (4S)-l-[4- H]homoserine established that cysteine must add to the si face of the vinyl-... 

Fig. 7.3. Stereochemical course of the 5-enolpyruvylshikimate 3-phosphate synthase reaction (adapted with permission from Asano et al., 1985, copyright 1985, American Chemical Society).

Asano, Y., J. J. Lee, T. L. SHffiH, F. Spreahco, C. Kowal, and H. G. Floss, Stereochemical course of the enol pyruvylshimi-mate-3-phosphate synthase, chorismate mutase, and anthrinilate synthase, J. Am. Chem. Soc., 107, 4314-4320 (1985). 

O Sullivan MC, Schwab JM, Zabriskie TM, Helms GL, Vederas JC. Reevaluation of the stereochemical courses of the allylic reairangemenc and the double bond reduction catalyzed by the Brevibacterium ammaniagenes fatty acid synthase. J Amer Chem Soc 1991 113 3997-3998. 

Fu H, McDaniel R, Hopwood DA, Khosla C. Engineered biosynthesis of novel polyketides Stereochemical course of two reactions catalyzed by a polyketide synthase. Biochem 1994 33 9321-9526. 

Fig. 1. Reaction mechanism and stereochemical course of the conversion of SAM to ACC catalyzed by the pyridox-al phosphate (PLP)-dependent ACC synthase. C-3 ( ) of the L-methionine portion of SAM becomes the pro-(R) methylene group of ACC. whereas the two hydrogens attached to C-3.4 of the methionine moiety in the cis-configuration yield cis-ACC...

As presented in this chapter, today, much is known about the process of terpene biosynthesis. The accumulated knowledge includes a detailed picture about the biosynthesis of the terpenoid monomers IPP and DMAPP either via the mevalonate or the DXP route and their interconversion by isomerases. Also, the stereochemical courses and enzyme mechanisms of all transformations have been largely elucidated. Especially the recently obtained structural data of prenyltransferases and various kinds of terpene synthases resulted in an evolutionary model that involves six domains (a, P, 7,8, e, and Q for the biosynthesis of linear polyisoprenoids from IPP and DMAPP and their subsequent transformation into (poly)cyclic terpenes. All these insights may open up new chances in controlling terpene biosynthesis, e.g., by directed evolution of terpene cyclases or domain swaps in multi-domain enzymes for the production of new terpenes, reconstitution of terpene biosynthetic pathways in heterologous hosts for production optimization, or targeted inhibitirm of pathways in pathogens for disease control. 

The steric course at during the normal y-replacement and abnormal y-ehmina-tion-deamination reactions catalysed by cystathionine-y-synthase has been deduced in an elegant series of experiments described by Walsh and coworkers. An important aid in this stereochemical investigation was the observation that L-vinylglycine [88]... 

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