Catalyzes the NADPH-dependent reduction of carbonyl compounds to their corresponding alcohols. Has low NADPH-dependent oxidoreductase activity (PubMed:18983987). Acts on several orthoquinones, acts as well on non-quinone compounds, such as isatin or on the anticancer drug oracin. Best substrates for CBR3 is 1,2- naphthoquinone, hence could play a role in protection against cytotoxicity of exogenous quinones. Exerts activity toward ortho-quinones but not paraquinones. No endogenous substrate for CBR3 except isatin has been identified (By similarity). a secondary alcohol + NADP(+) = a ketone + H(+) + NADPH a quinone + H(+) + NADPH = a quinol + NADP(+) kcat is 14 min(-1) with 4-benzoylpyridine as substrate (PubMed:18983987). kcat is 0.030 min(-1) with menadione as substrate (PubMed:18983987). 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 (By similarity). Results of later studies showed that CBR3 possesses very low or no activity toward menadione (PubMed:18983987).