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:18493841, PubMed:15537833, 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). a secondary alcohol + NADP(+) = a ketone + H(+) + NADPH a quinone + H(+) + NADPH = a quinol + NADP(+) kcat is 0.55 min(-1) with menadione as substrate (PubMed:18493841). kcat is 0.70 min(-1) with 4-benzoylpyridine as substrate (PubMed:18493841). kcat is 0.59 min(-1) with 4-nitorobenzaldehyde as substrate (PubMed:18493841). Optimum pH is 5.5-7. Detected in ovary, pancreas, intestine, colon, kidney, brain, thymus, lung, heart, liver, spleen, leukocyte, prostate and testis. Belongs to the short-chain dehydrogenases/reductases (SDR) family. There are conflicting results on the ability of CBR3 to metabolize menadione. Although menadione was originally reported as a good substrate of CBR3 (PubMed:15537833), results of later studies showed that CBR3 possesses very low or no activity toward menadione (PubMed:19841672,PubMed:18493841).