Tissue carboxylesterase activity of rainbow trout

• Published in: Environmental toxicology and chemistry 1999-11, Vol.18 (11), p.2506-2511
• Main Authors: Barron, Mace G., Charron, Kem A., Stott, William T., Duvall, Stephanie E.
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biotransformation; carboxylesterase; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Enzyme kinetics; Fish; Fundamental and applied biological sciences. Psychology; Oncorhynchus mykiss; Xenobiotic metabolism
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1002/etc.5620181117

The activity of carboxylesterase (CaE), a class of nonspecific serine hydrolases, was evaluated in vitro in tissues and microsomes of rainbow trout and compared to esterase activity in rats, other fish species, and embryo to adult life stages of trout. Trout gill and liver microsomes exhibited substantial CaE activity and limited variation over the range of 2 to 40°C, with a temperature optimum of approximately 22°C. Trout sera and rat liver microsomes exhibited a temperature optimum of approximately 35 to 40°C. The CaE of trout liver (maximum reaction rate [Vmax] = 672 nmol/min/mg microsomal protein) was four times less than in rats. Apparent Michaelis constant (Km) values ranged from 28 (trout liver) to 214 (trout sera) μM. Values of Vmax/Km suggested that in vivo CaE activity of trout liver would be about three times higher than serum, 135 times higher than gill, and three times lower than rat liver. The CaE activity in whole rainbow trout homogenates significantly increased 300% per gram of tissue to 1,200% per milligram of protein between the yolk‐sac and juvenile stages. The CaE activity of whole fish homogenates was not significantly different in juvenile rainbow trout, channel catfish, fathead minnows, and bluegill. The results demonstrate that rainbow trout had high esterase activity over a broad range of temperatures, that CaE activity significantly increased between the yolk‐sac and juvenile life stages, and that variation between the CaE activity in trout and three other families of freshwater fish was limited. The CaE activity in fish is expected to substantially influence the accumulation and toxicity of pesticides and other esters entering the aquatic environment.