Cytoplasmic potassium Channel subunit that modulates the characteristics of the Channel-forming alpha-subunits (PubMed: 7649300, PubMed: 11825900). Contributes to the regulation of nerve signaling, and prevents neuronal hyperexcitability (By similarity). Promotes expression of the pore-forming alpha subunits at the cell membrane, and thereby increases Channel activity (By similarity). Promotes potassium Channel closure via a mechanism that does not involve physical obstruction of the Channel pore (PubMed: 7649300, PubMed: 11825900). Promotes KCNA4 Channel closure (PubMed: 7649300, PubMed: 11825900). Modulates the functional properties of KCNA5 (By similarity). Enhances KCNB2 Channel activity (By similarity). Binds NADPH and has NADPH-dependent aldoketoreductase activity (By similarity). 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) (By similarity).