Cytoplasmic potassium channel subunit that modulates the characteristics of the channel-forming alpha-subunits. Contributes to the regulation of nerve signaling, and prevents neuronal hyperexcitability. Promotes expression of the pore-forming alpha subunits at the cell membrane, and thereby increases channel activity. Promotes potassium channel closure via a mechanism that does not involve physical obstruction of the channel pore. Promotes KCNA4 channel closure. Modulates the functional properties of KCNA5. Enhances KCNB2 channel activity. Binds NADPH and has NADPH-dependent aldoketoreductase activity. Has broad substrate specificity and can catalyze the reduction of methylglyoxal, 9,10-phenanthrenequinone, prostaglandin J2, 4-nitrobenzaldehyde, 4-nitroacetophenone and 4-oxo-trans-2-nonenal (in vitro).

> 90% as determined by SDS-PAGE.