Esterases rabbit serum

Phosphinates are a class of organophosphorus compounds, the metabolism of which has received less attention than that of phosphates (see above) or phosphorothioates and P-halidc compounds (see below). Many phosphinates are rapid but transient inhibitors of acetylcholinesterase and carboxyl-esterases. And like organophosphates and phosphonates, phosphinates are substrates of arylesterases (EC 3.1.1.2). This is exemplified by 4-nitrophen-yl ethyl(phenyl)phosphinate (9.62), whose (-)-enantiomer was hydrolyzed by rabbit serum arylesterase almost 10 times faster than the (+)-enantiomer [133],... 

Esterases in serum from rabbits and to a lesser extent humans can convert diacetyl chloramphenicol back to an active antibiotic. Therefore, in vitro findings may not accurately reflect the level of chloramphenicol resistance by chloramphenicol acetyltransferase-bearing bacteria in vivo, when growth media supplemented with serum are used (58). 

Main et al. (M5) found high concentrations of a butyrylcholine esterase, of relative molecular mass 83,000 daltons, in pooled rabbit serum. This was unexpected, since rabbit serum is classed with those mammalian sera that have low cholinesterase activities (A25, E2). Substrate specificity confirmed that the enzyme was a butyrylcholine esterase. Moreover, the active site concentration of the enzyme was five times that found for pooled horse serum, which is a rich source of the enzyme. The known fact that some rabbits can metabolize atropine, whereas others are unable to do so, can be explained by the presence or absence of serum atropinase, which is a genetic trait. Perhaps the subunit-sized butyrylcholine esterase is characteristic of some rabbits, but absent in others This seems probable according to Ellis (E9) and Koelle... 

The above mentioned investigations revealed that the lipase-mediated hydrolysis proceeds at higher reaction rate and, in many cases with better selectivity, if butanoates or pentanoates are employed as substrates instead of acetates. However, the use of enzymatic deacylations is by no means restricted to simple alkanoates. An illustrative and impressive example is found in the hydrolysis of generally base-stable carbohydrate pivaloylates using an esterase from rabbit serum (ERS)[214—217]. For instance, the biocatalyst selectively splits off the 6-pivaloyl group from a-methyl... 

There is less information about the metabolism of other tropane alkaloids but for those that are esters (e.g. hyoscyamine, scopolamine) hydrolysis of the ester bond takes place to some extent, yielding bases, which may be further transformed [45, 46], Rabbit serum has been found to have esterases that are relatively specific for esters of tropic acid, and this may account for the ability of rabbits to feed with impunity on leaves of Atropa belladona [47]. Mice transform released tropic acid to a glucuronide [48]. Oxidation also occurs, both in rats and humans, with the production of N-oxides and oxidative removal of the N-methyl group to make nor-derivatives [45,46]. 

Savin, P. B. and Glick, D. (1943) Hydrolysis of atropine by esterase present in rabbit serum. Proc. Natl. Acad. Sci. USA 29, 55. 

An interesting report by P an and Jegier noted an increase in serum trypsin protein esterase in association with pulmonaiy vascular lesions in rabbits chronically exposed to ozone at 0.4 ppm. This serum a,-macroglobulin, which is synthesized in the liver, has been reported to be increased in human vascular disorders, but its physiologic significance is unknown. 

Increased serum trypsin protein Rabbit esterase... 

Van Zutphen LFM (1974) Serum esterase genetics in rabbits. I. Phenotypic variation of the prealbumin esterases and classification of atropinesterase and cocainesterase. Biochem Genetics 12 309-326... 

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