The function of CBR3 (carbonyl reductase 3, ENSG00000159231) is as follows. Catalyzes the NADPH-dependent reduction of carbonyl compounds to their corresponding alcohols (PubMed:18493841). Has low NADPH- dependent oxidoreductase activity. Acts on several orthoquinones, acts as well on non-quinone compounds, such as isatin or on the anticancer drug oracin (PubMed:15537833, PubMed:18493841, PubMed:19841672). Best substrates for CBR3 is 1,2- naphthoquinone, hence could play a role in protection against cytotoxicity of exogenous quinones (PubMed:19841672). Exerts activity toward ortho-quinones but not paraquinones. No endogenous substrate for CBR3 except isatin has been identified (PubMed:19841672). {ECO:0000269|PubMed:15537833, ECO:0000269|PubMed:18493841, ECO:0000269|PubMed:19841672}.