Transcriptomics‐based systematic identification and tissue‐specific distribution of cytochrome P450 genes in Carassius auratus

Abstract

Cytochrome P450 (CYP450) enzymes are superfamily with a terminal oxidase of the single-chain B group and iron protoporphyrin as a prosthetic group. Due to the similar structure to haem and an absorption peak at 450 nm after interacting with CO, this superfamily was named CYP450 enzyme. CYP450, as one of the important metabolic enzymes, is involved in the detoxification of exogenous chemicals such as drugs and environmental toxicity, and in the metabolism of endogenous substrates, such as steroids, polyunsaturated fatty acids and fat-soluble vitamins (Nebert et al., 2004). CYP450 enzyme system, an electron transport system, is constituted of flavin protein, haem protein and phospholipid, with flavin protein consisting of nicotinamide adenine dinucleotide phosphate (NADPH)-b5 and NADPH-P450 reductase, and haem protein containing b5 and P450.CYP450 gene superfamily (CYPs) is an ancient gene superfamily and is widely distributed in various organs and tissues of animals and plants (Liao et al., 2017). However, its distribution varies from species to species. In mammals, CYPs are most widely distributed in liver, kidney, brain, pancreas, skin, intestine and lung (Zhu & Lou, 2004).In fish, CYP450 is mainly expressed in liver, followed by intestine, kidney and gill (Itakura et al., 2005).CYPs genes are induced by polycyclic aromatic hydrocarbons (PAHs), pesticides and heavy metals. In fish, numerous studies of the CYP1A have demonstrated its utility as a biomarker for aquatic pollution. In Carassius auratus, it has been shown that phoxim, an organophosphorus pesticide, can induce the down-regulation of CYP1A and CYP3A messenger RNA (mRNA) expression levels in liver.