Cytoplasmic potassium channel subunit that modulates the characteristics of the channel-forming alpha-subunits (By similarity). Modulates action potentials via its effect on the pore-forming alpha subunits (By similarity). Promotes expression of the pore-forming alpha subunits at the cell membrane, and thereby increases channel activity (By similarity). Mediates closure of delayed rectifier potassium channels by physically obstructing the pore via its N-terminal domain and increases the speed of channel closure for other family members (By similarity). Promotes the closure of KCNA1, KCNA2 and KCNA5 channels (By similarity). Accelerates KCNA4 channel closure (By similarity). Accelerates the closure of heteromeric channels formed by KCNA1 and KCNA4 (By similarity). Accelerates the closure of heteromeric channels formed by KCNA2, KCNA5 and KCNA6 (By similarity). Enhances KCNB1 and KCNB2 channel activity (By similarity). Binds NADPH; this is required for efficient down-regulation of potassium channel activity (By similarity). Has NADPH-dependent aldoketoreductase activity (By similarity). Oxidation of the bound NADPH strongly decreases N-type inactivation of potassium channel activity (By similarity). Homotetramer (By similarity). Interaction with tetrameric potassium channel alpha subunits gives rise to a heterooctamer (Probable). Identified in potassium channel complexes containing KCNA1, KCNA2, KCNA4, KCNA5, KCNA6, KCNAB1 and KCNAB2 (By similarity). Interacts with KCNA1 (By similarity). Interacts with the dimer formed by GNB1 and GNG2; this enhances KCNA1 binding (By similarity). Interacts with KCNA4 (By similarity). Interacts with KCNA5 (By similarity). Interacts with KCNB2 (By similarity). Interacts with SQSTM1 (By similarity). Part of a complex containing KCNA1, KCNA4 and LGI1; interaction with LGI1 inhibits down-regulation of KCNA1 channel activity (By similarity). Recruited to the cytoplasmic side of the cell membrane via its interaction with pore-forming potassium channel alpha subunits. The N-terminal domain of the beta subunit mediates closure of delayed rectifier potassium channels by physically obstructing the pore. Belongs to the shaker potassium channel beta subunit family.