MaxiK(beta) subunit 1 consists of two putative transmembrane domains, an extracellular loop containing three consensus sequences for N-linked glycosylation and four cysteine residues that might form disulfide bridges. MaxiK(beta) subunit 1, one of four subunits in the MaxiK(beta) family, is expressed predominately in smooth muscle tissue but is also found in brain, liver and lymphatic tissues. MaxiK(beta) subunit 1 associates with MaxiK(alpha) to form a calcium-activated potassium channel (also designated MaxiK and BK channel). MaxiK(beta) subunit 1 increases the sensitivity of the MaxiK(alpha) to calcium and voltage. The MaxiK(alpha)/(beta)1 channel is the most sensitive of all Maxi channels to calcium. MaxiK(beta) plays an important role in vasoregulation by controlling the sensitivity of MaxiK channels to calcium, which leads to the proper amount of arterial relaxation.