Characterization of catalytic efficiency parameters of brain cholinesterases in tropical fish

Abstract

Brain cholinesterases from four fish (Arapaima gigas, Colossoma macropomum, Rachycentron canadum and Oreochromis niloticus) were characterized using specific substrates and selective inhibitors. Parameters of catalytic efficiency such as activation energy (AE), k(cat) and k(cat)/k(m) as well as rate enhancements produced by these enzymes were estimated by a method using crude extracts described here. Despite the BChE-like activity, specific substrate kinetic analysis pointed to the existence of only acetylcholinesterase (AChE) in brain of the species studied. Selective inhibition suggests that C. macropomum brain AChE presents atypical activity regarding its behavior in the presence of selective inhibitors. AE data showed that the enzymes increased the rate of reactions up to 10(12) in relation to the uncatalyzed reactions. Zymograms showed the presence of AChE isoforms with molecular weights ranging from 202 to 299 kDa. Values of k(cat) and k(cat)/k(m) were similar to those found in the literature.

Impacts of Agricultural Toxicity on Non-Target Organisms in Aquatic Ecosystem

“…The use of enzymes as biomarkers is based on inhibitory or inductive interference caused by contaminants in their catalytic activity. Most of these toxic compounds have a high affinity for electron pairs found in the amino acids that form the enzymes, such as the sulfhydryl -SH groups and other functional groups from the catalytic site [5,27]. Among the main enzymes used extensively for this purpose, cholinesterase enzymes stand out (ChEs; EC 3.1.1.x).…”

“…has been widely studied in aquatic organisms and proposed for use in monitoring programs, given its sensitivity [5,6]. On the other hand, BChE predominates in plasma, liver, neuroglia, pancreas, and digestive tract walls.…”

“…These toxic substances have the potential to cause various biochemical and genetic injuries to non-target organisms. Carbamates and organophosphates, for example, are potent inhibitors of the acetylcholinesterase enzyme, which damages the nervous system of an exposed organism [5,6]. This enzyme acts in the hydrolysis of the acetylcholine neurotransmitter in cholinergic synapses.…”

Potential Toxicity in Crucian Carp Following Exposure to Metallic Nanoparticles of Copper, Chromium, and Their Mixtures: A Comparative Study

“…The enzyme of AChE plays a vital role in hydrolysis of the neurotransmitter acetylcholine to ensure the intermittence of nerve impulses responsible for neuronal communication [27]. Changes of AChE enzymatic activity may alter many physiological functions in aquatic organisms, such as locomotion, predator evasion, prey location, and orientation [28].…”

Genotoxic effect of heavy metals on Nile tilapia (Oreochromis niloticus) species in an urban river in northeastern Brazil

“…In Northeast Brazil, it was introduced in 1971 (Lovshin, 2000). According to Assis et al (2014), tilapia are highly resistant to impacted environments and can tolerate low levels of oxygen. Furthermore, they have good nutritional characteristics, such as tasty meat with low-fat content (0,9 g/100 g of meat) and calories (172 Kcal/100 g of meat).…”