Serine reaction

Figure 15.6 Formation of methyl tetrahydrofolate and SAM from serine. Reaction (1) is described in Appendix 8.3. Reaction (ii) is Figure 15.5 and the several reactions represent in reaction (iv) are discribed in Figure 15.4.

Fig. 12. Normalized spectra (—) and difference spectrum (—) compmaring the 425 nm cqff, transient species with the quasi-stable 420 nm 02 species formed in the z-serine reactions. The spectrum labeled 02 scr nc is the final spectrum at 1970 ms derived from RSSF data set for the reaction of the isolated 02-subunit with i-serine (data not shown). The spectrum labeled a232-serine is the first scan derived from a RSSF data set for the reaction of 40 mM l-serine with the ct202-bienzyme complex. These spectra were baseline zeroed and normalized by adjusting each spectrum to the same amplitude. The difference spectrum was generated by subtracting the normalized 02-serine final spectrum from the normalized a202-serine spectrum. [Taken from Drewe and Dunn (85) with permission.]...

Fig. 5. Kinetics of serine reaction with tryptophan synthase. (A) The change in fluorescence at 500 nm was measured by stopped-flow after mixing enzyme (2 fiM) with serine (500 fiM). The smooth line represents a fit to a double exponential with rates of 150 and 40 sec. (B) The serine concentration dependence of the fast and slow phases of the reaction are fit to the equations as described in the text. Reproduced with permission from (32).

FIG. 2. The imcraction of ACh, CM, and OP compounds with the active. site serine of AChE and BuChE. Reaction I represents the formation of a stable Michaelis complex and the beginning of the nucleophilic attack of the serine. Reaction 2 represents the acylation of the active site serine, coupled with the relca.se of the fir.st reaction product or leaving group. Reaction 3 begins the nucleophilic attack of a hydroxyl ion, which leads to the regeneration of active enzyme (reaction 4). 

This leads us to another pathway for the catabolism of glycine which must be of very great significance. This is the conversion of glycine to serine (reaction 4). The subsequent fate becomes that of serine, which is discussed in the next section. 

That the reaction given in Fig. 2 for the mechanism of deamination is correct is supported by the failure of the enzyme preparations to deaminate phosphoserine and 0-ethers of serine and the isolation of pyruvic acid from the serine reaction mixtures. "... 

Thus, whereas in mammalian tissue phosphatidyl ethanolamine is formed by way of CDP-ethanolamine (Reaction 19), and incidentally may be methylated to form lecithin (Figure 2), in E, coli phosphatidyl ethanolamine is derived from phosphatidyl serine (Reaction 22), which is formed by way of CDP-diglyceride (Reaction 21, Figure 4). 

Ketones from glycol monoesters Serin reaction... 

The necessity for tetrahydrofolic acid and pyridoxal phosphate in the glycine-serine reaction has subsequently been firmly established and the locus of action of these cofactors elucidated by more searching experiments of many investigators 34-44)-... 

The reaction between esterase and phosphorus inhibitor (109) is bimolecular, of the weU-known S 2 type, and represents the attack of a nucleophilic serine hydroxyl with a neighboring imida2ole ring of a histidine residue at the active site, on the electrophilic phosphorus atom, and mimics the normal three-step reaction that takes place between enzyme and substrate (reaction ). 

Enzymatic Process. Chemically synthesized substrates can be converted to the corresponding amino acids by the catalytic action of an enzyme or the microbial cells as an enzyme source, t - Alanine production from L-aspartic acid, L-aspartic acid production from fumaric acid, L-cysteine production from DL-2-aminothiazoline-4-catboxyhc acid, D-phenylglycine (and D-/> -hydtoxyphenylglycine) production from DL-phenyUiydantoin (and DL-/)-hydroxyphenylhydantoin), and L-tryptophan production from indole and DL-serine have been in operation as commercial processes. Some of the other processes shown in Table 10 are at a technical level high enough to be useful for commercial production (24). Representative chemical reactions used ia the enzymatic process are shown ia Figure 6. 

Protein G. This vitamin K-dependent glycoproteia serine protease zymogen is produced ia the Hver. It is an anticoagulant with species specificity (19—21). Proteia C is activated to Proteia by thrombomodulin, a proteia that resides on the surface of endothefial cells, plus thrombin ia the presence of calcium. In its active form, Proteia selectively iaactivates, by proteolytic degradation. Factors V, Va, VIII, and Villa. In this reaction the efficiency of Proteia is enhanced by complex formation with free Proteia S. la additioa, Proteia activates tissue plasminogen activator, which... 

CF3CO2H, PhSCH3, 25°, 3 h. ° The use of dimethyl sulfide or anisole as a cation scavenger was not as effective because of side reactions. Benzyl ethers of serine and threonine were slowly cleaved (30% in 3 h complete cleavage in 30 h). The use of pentamethylbenzene had been shown to increase the rate of deprotection of 0-Bn-tyrosine. ... 

The serine proteinases have been very extensively studied, both by kinetic methods in solution and by x-ray structural studies to high resolution. From all these studies the following reaction mechanism has emerged. 

Absolute configurations of the amino acids are referenced to D- and L-glyceraldehyde on the basis of chemical transformations that can convert the molecule of interest to either of these reference isomeric structures. In such reactions, the stereochemical consequences for the asymmetric centers must be understood for each reaction step. Propose a sequence of reactions that would demonstrate that l( —)-serine is stereochemically related to l( —)-glyceraldehyde. 

FIGURE 10.10 The reaction of tridated sodium borohydride with the aspartyl phosphate at the active site of Na, K -ATPase. Acid hydrolysis of the enzyme following phosphorylation and sodium borohydride treatment yields a tripeptide containing serine, homoserine (derived from the aspartyl-phosphate), and lysine as shown. The site of phosphorylation is Asp" in the large cytoplasmic domain of the ATPase. 

X-ray crystallographic studies of serine protease complexes with transition-state analogs have shown how chymotrypsin stabilizes the tetrahedral oxyanion transition states (structures (c) and (g) in Figure 16.24) of the protease reaction. The amide nitrogens of Ser and Gly form an oxyanion hole in which the substrate carbonyl oxygen is hydrogen-bonded to the amide N-H groups. 

The first domain of one subunit of the fatty acid synthase interacts with the second and third domains of the other subunit that is, the subunits are arranged in a head-to-tail fashion (Figure 25.9). The first step in the fatty acid synthase reaction is the formation of an acetyl-O-enzyme intermediate between the acetyl group of an acetyl-CoA and an active-site serine of the acetyl trails-... 

FIGURE 25.10 Acetyl units are covalently linked to a serine residue at the active site of the acetyl transferase in eukaryotes. A similar reaction links malonyl units to the malonyl transferase. 

Mammals synthesize phosphatidylserine (PS) in a calcium ion-dependent reaction involving aminoalcohol exchange (Figure 25.21). The enzyme catalyzing this reaction is associated with the endoplasmic reticulum and will accept phosphatidylethanolamine (PE) and other phospholipid substrates. A mitochondrial PS decarboxylase can subsequently convert PS to PE. No other pathway converting serine to ethanolamine has been found. 

FIGURE 25.25 Biosynthesis of sphingolipids in animals begins with the 3-ketosphinga-nine synthase reaction, a PLP-dependent condensation of palmitoyl-CoA and serine. Subsequent rednction of the keto group, acylation, and desatnration (via rednction of an electron acceptor, X) form ceramide, the precnrsor of other sphingolipids. 

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