The 83 kDa subunit binds and stabilizes the catalytic subunit at 37 degrees Celsius and keeps it in circulation. Under some circumstances it may be an allosteric modifier of the catalytic subunit. Tetramer of two catalytic chains and two glycosylated inactive chains. Whether or not any Cys residues participate in intrachain bonds is unknown, but they do not form interchain disulfide bonds with the 50 kDa catalytic subunit.