Base-exchange reactions

Phosphatidyl-ethanolamine-seririe transferase (base exchange reaction)... 

The primary pathway for synthesis of PS in mammalian tissues is provided by the base exchange reaction, in which the ethanolamins of PE is exchanged for free serine (see Figure 17.6). This reaction although reversible, is used primarily to produce the PS required for membrane synthesis. 

In prokaryotes, phosphatidylserine is made from CDP-diacylglycerol (see fig. 19.3). The enzyme for this reaction is absent in animal cells, which rely on a base exchange reaction in which serine and ethanolamine are interchanged (fig. 19.8). Although the reaction is reversible, it usually proceeds in the direction of phosphatidylserine synthesis. Phosphatidylserine can be converted back to phos-phatidylethanolamine by a decarboxylation reaction in the mitochondria. This may be the preferred route for phosphatidylethanolamine biosynthesis in some animal cells. Furthermore these two reactions (see fig. 19.8) establish a cycle that has the net effect of converting serine into ethanolamine. This is the main route for ethanolamine synthesis... 

In addition to its capability as a phosphodiesterase, this enzyme also was found by Yang et al. (1967) to possess transphosphatidylase activity (essentially a base exchange reaction) as illustrated in Figure 4-17. 

Vanselow AP (1932) Equilibria of the base-exchange reactions of bentonies, permutites, soil colloids and zeolites.- Soil Sci. 33... 

Figure 8.7. Reactions catalyzed byADP ribose cyclase (NAD glycohydrolase, EC 3.2.2.5). When the substrate is NADP, the base exchange reaction leads to the formation of nicotinic acid adenine dinucleotide phosphate.

There are two classes of thiaminase. Thiaminase I catalyzes a base exchange reaction between the thiazole moiety of thiamin and a variety of bases, commonly primary, secondary, or tertiary amines, but also nicotincimide and other pyridine derivatives, and sometimes proline tmd sulfhydryl compounds. Thiaminase I is relatively widespread in a veuiety of microorgcmisms, plcmts, cmd fish. In addition to depleting thiamin, the products of base exchange catedyzed by thiaminase I eire structured emedogs of the viteimin and may have antagonistic effects (Edwin and Jackman, 1970). Similarly, the neurotoxic effects of the antibiotic metronidazole, which is a thiazole, may be fi om its activity as a substrate for thieiminase I, forming thiamin antimetabolites (Alston emd Abeles, 1987). 

Greenhill, J. V. and Ramli, M., A base exchange reaction between a 1,2-diketo-bis Mannich base and o-phenylenediatninc. Tetrahedron Lett., 4059, 1973. 

Figure 7 The variations of chloride, calcium, strontium (in mgL ), and Sr/ Sr ratios during intrusion of seawater into the coastal aquifer of Salinas Valley, California, USA. Note the linear relationships between all constituents, which indicates conservative mixing relationships between freshwater and modified seawater. These relationships suggest that base-exchange reactions occur at early stage of seawater intrusion and that Sr in exchange sites has a high Sr/ Sr ratio (source Vengosh et aL, 2002a).

Barshad, I., 1948. Vermiculite and its relation to biotite as revealed by base exchange reactions, X-ray analyses, differential thermal analysis curves, and water contents. Am. Mineral. 33 655—678. 

Phosphatidylserine makes up 10% of phospholipids in mammals. This phospholipid is synthesized in a base-exchange reaction of serine with phosphatidylcholine or phosphatidylethanolamine. In the reaction, serine replaces choline or ethanolamine. 

To overcome the problem with the charges on acids and bases, we can be less ambitious, and make more restricted comparisons of acidity and basicity.233 To obtain a useful quantitative measure of the hardness of acids and bases, we apply the concept in Equation 3.1 to the acid base exchange reaction in Equation 3.7, which will take place from left to right if A1 and B1 are the harder acids and bases relative to A2 and B2. 

All PLDs characterized thus far act by a phosphatidate exchange reaction that involves a covalent phosphatidyl-enzyme as an intermediate [33]. For this reason, PLD can catalyze a base-exchange reaction in which alcohols can substitute for water as the... 

Nicotinamide l,iV -ethenoadenine dinucleotide, prepared from NAD+ and chloroacetaldehyde, has been converted into 3-aminopyridine l,A -etheno-adenine dinucleotide (4) by a pyridine base exchange reaction which was catalysed by the venom of Bungarus fasciatus. Yeast alcohol dehydrogenase was... 

Translation of the Hard and Soft Acids and Bases principle into a readily applicable formal expression has never been achieved. Huheey suggested, that the driving force to the HSAB rule is a strong hard-hard interaction only, in a set of an acid/base exchange reaction [18]. Nalewajski presented a thorough discussion of that topic [57] and summarized older concepts. Soft-soft interaction is predominantly covalent, whereas hard-hard interaction occurs through ionic forces. The classical formula for energy (Eq. 17) explains why a soft-soft interaction is favored over a soft-hard one the favorable hard-hard situation cannot be accounted for by Eq. 17. 

Interaction Energy for Hard-Soft Add-Base Exchange Reactions Involving Polyatomic Molecules... 

Let us consider the generalized acid-base exchange reaction as follows ... 

We have already applied this formula for the correlation of the reaction surface of a number of well known acid-base exchange reactions involving diatomic molecules using the global hardness data of the corresponding diatomic molecules computed through our algorithm. 

A look at the Eqs. 13.23 and 13.29 reveals that the hardness difference is directly related to the reaction energy of the acid/base exchange reactions. It may be represented by ... 

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