Esterase activities

The cAMP formed by adenylyl cyclase (Figure 15.20) does not persist because 5 -phosphodiesterase activity prevalent in cells hydrolyzes cAMP to give 5 -AMP. Caffeine inhibits 5 -phosphodi-esterase activity. Describe the effects on glycogen phosphorylase activity that arise as a consequence of drinking lots of caffeinated coffee. 

Basic Aspects of Polyelectrolytes Retaining Esterase Activities. . . . 172... 

Basic Aspects of Polyelectrolytes Retaining Esterase Activities... 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

FIGU RE 2.10 Plasma A-esterase activities of birds and mammals. Activities were originally measured as nanomoles product per milliliter of serum per minute, but they have been converted to relative activities (male rat = 1) and plotted on a log scale. Each point represents a mean value for a single species. Substrates , paraoxon , pirimiphos-methyl oxon. Vertical hues indicate limits of detection, and all points plotted to the left of them are for species in which no activity was detected. (Activities in the male rat were 61 4 and 2020 130 for paraoxon and pirimiphos-methyl oxon, respectively.) (From Walker 1994a in Hodgson and Levi 1994.)... 

The organophosphorons insecticides dimethoate and diazinon are mnch more toxic to insects (e.g., housefly) than they are to the rat or other mammals. A major factor responsible for this is rapid detoxication of the active oxon forms of these insecticides by A-esterases of mammals. Insects in general appear to have no A-esterase activity or, at best, low A-esterase activity (some earlier stndies confnsed A-esterase activity with B-esterase activity) (Walker 1994b). Diazinon also shows marked selectivity between birds and mammals, which has been explained on the gronnds of rapid detoxication by A-esterase in mammals, an activity that is absent from the blood of most species of birds (see Section 23.23). The related OP insecticides pirimiphos methyl and pirimiphos ethyl show similar selectivity between birds and mammals. Pyrethroid insecticides are highly selective between insects and mammals, and this has been attributed to faster metabolic detoxication by mammals and greater sensitivity of target (Na+ channel) in insects. 

Brealey, C.J., Walker, C.H., and Baldwin, B.C. (1980). A Esterase activities in relation to differential toxicity of pirimiphos-methyl. Pesticide Science 11, 546-554. 

Mackness, M.I., Walker, C.H, Rowlands, D.G. et al. (1982). Esterase activity in homogenates of 3 strains of rust red flour beetle. Comparative Biochemistry and Physiology 74C, 65-68. 

Parker, P.J.-A. and Callaghan, A. (1997). Esterase activity and allele frequency in field populations of Simulium equinum exposed to organophosphate pollution. Environmental Toxicology and Chemistry 16, 2550-2555. 

The growth requirements outlined above express themselves in growth itself through the less tangible but fundamental necessity of energy which is provided by metabolism. Not all metabolic reactions, however, provide energy esterase activity is an example of one that does not. 

In media selective for enterobacteria a surface-active agent is the main selector, whereas in staphylococcal medium sodium and lithium chlorides are the selectors staphylococci are tolerant of salt concentrations to around 7.5%. Mannitol salt, Baird-Parker (BP) and Vogel-Johnson (VJ) media are three examples of selective staphyloccocal media. Beside salt concentration the other principles are the use of a selective carbon source, mannitol or sodium pyruvate together with a buffer plus acid-base indicator for visualizing metabolic activity and, by inference, growth. BP medium also contains egg yolk the lecithin (phospholipid) in this is hydrolysed by staphylococcal (esterase) activity so that organisms are surrounded by a cleared zone in the otherwise opaque medium. The United States Pharmacopeia (1990) includes a test for staphylococci in pharmaceutical products, whereas the British Pharmacopoeia (1993) does not. 

Pectin esterase activity was assayed by measuring the decreasing of pH in the reaction mixture which equal to methanol liberated by the method of Wood, et al. (11). 

SDS-PAGE was performed by the method of Laemmli [17]. The methods for native PAGE, isoelectric focussing, detection of esterase activity in electrophoresis gels, and assays for protein glycosylation have been described elsewhere [5]. 

Changes in extracellular esterase activity with incubation time. Esterase activities were assayed using the following methyl esters MCA ( ), MpCA ( ), MSA(a) and MFA (a). 

FMC. 1991a. The effects of Durad 125 on serum cholinesterase and brain neuropathy. Target esterase activity in male Long-Evans rats. Study No 64460. FMC Corporation, Princeton, NJ. 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

Table 2 Reference Values of Lymphocyte and Platelet Neuropathy Target Esterase Activity...

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