Disclosed is a method for purifying a protein, comprising steps of: preparing a sample containing a fusion protein containing an amino acid sequence of a peptide tag and an amino acid sequence of a target protein; and separating contaminant proteins contained with the fusion protein in the sample and the fusion protein in the sample, wherein the peptide tag contains 12 or more acidic amino acid residues.

The present invention provides a method capable of effectively treating various diseases associated with energy excess, such as obesity, diabetes, metabolic syndromes, degenerative diseases and mitochrondrial dysfunction-related diseases, via elevation of an NAD(P)⁺ZNAD(P)H ratio by increasing an NAD(P)⁺ concentration in vivo or in vitro through use of NAD(P)H as a substrate or coenzyme by oxidoreductase such as NAD(P)H:quinine oxidoreductase (NQO1), a method of screening a drug for the same and a therapeutic drug.

Compounds of the general formula: wherein R is H, an acyl group or a hydrocarbyl group containing up to 6 carbon atoms, have cytotoxic activity against several tumours. The 4-hydroxylamino compound can be obtained directly from the corresponding 2,4-dinitro compound by selective chemical reduction or by the action of a nitroreductase obtainable from Walker tumour cells. The 2,4-dinitro compound is substantially devoid of cytotoxic activity except in relation to Walker tumour cells and hence can act as a prodrug in regimes where a prodrug is localised in vivo in the regions of a tumour to be treated and is then activated to the cytotoxic 4-hydroxylamino compound under the influence of the enzyme.