alpha 2-Macroglobulin bait region integrity. Role in determining fast-form structure

To determine whether integrity of the bait region affects the structure of the remainder of human alpha 2-macroglobulin (alpha 2M), we have determined the separation between cysteine residues in a methylamine-reacted fast-form of alpha 2M. From reduction in fluorescence intensity of covalently-bound donor fluorophore caused by proximity to an acceptor, a separation of 35 +/- 8 A was calculated, which is identical to a previously determined value for proteinase-treated fast-form alpha 2M. This indicates that although bait region cleavage is the physiological route to conformational change in alpha 2M, bait region integrity per se does not significantly affect the structure of fast-form alpha 2M.