Insecticide liver microsomes from

Figure 1. Cytochrome P-450 contents in liver microsomes from insecticide-resistant and -susceptible mosquitofish...

Figure 2. Specific activity of NADPH-Cytochrome c reductase in liver microsomes from insecticide-resistant and -susceptible mosquitofish. A unit (U) of enzyme activity is defined as 1 pmol product formed/min.

Flupyrazofos (9.75) is an insecticide whose relatively simple metabolic scheme appears quite informative. Indeed, rat liver microsomes formed the oxon analogue as the only detectable primary metabolite [150], The latter then underwent chemical hydrolysis to the dephosphorylated phenol with a tm value of ca. 50 min at pH 7.4 and 37°. In rat liver microsomes, the phenol appeared to be produced exclusively from flupyrazofos oxon, indicating the resistance of flupyrazofos toward chemical hydrolysis. 

Blood and various organs of humans and other animals contain esterases capable of acetylsalicylic acid hydrolysis. A comparative study has shown that the liver is the most active tissue in all animal species studied except for the guinea pig, in which the kidney is more than twice as active as the liver. Human liver is least active the enzyme in guinea pig liver is the most active. The relatively low toxicity of some of the new synthetic pyrethroid insecticides appears to be related to the ability of mammals to hydrolyze their carboxyester linkages. Thus mouse liver microsomes catalyzing (+)-/runs-resin e 111ri n hydrolysis are more than 30-fold more active than insect microsomal preparations. The relative rates of hydrolysis of this substrate in enzyme preparations from various species are mouse > > milkweed bug > > cockroach > > cabbage looper > housefly. 

A novel biomarker of OP insecticide exposure, egasyn, is an accessory protein of glucuronidase (BG) in the liver micro-somes (Swank and Paigen, 1973). Mcdda et al. (1987) reported that egasyn has esterase activity and it is one of the carboxylesterase (CarbE) isozymes. Later, Hosokawa and coworkers (1987, 1990) purified three CarbE isozymes (RLl, RL2, and RHl) from rat liver microsomes, and ega,syn was identified as RL2 isozyme. In 1998, Satoh and Hosokawa proposed a new das.sificalion of CarbE isozymes based on the molecular homology of the individual esterase isozymes. 

In many instances, such as in studies of metabolism or degradation where the sensitivity is not so important, TLC and radioscanning provide a quick and simple technique for the identification and quantitation of radiolabeled metabolic products. An example of a radiochromatogram scan is shown in Fig. 2.13 for the analysis of some metabolites of the insecticide ethyl parathion in a microsomal enzyme preparation from rat liver [SI]. 

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