In this report we demonstrate that human a2-macroglobulin (a2M)reacts with deglycosylated ricin A chain (dgA) and its immunotoxins toform high molecular weight complexes (molecular mass approximately800 kDa). This interaction has a /i/2at 37°Cof 5 h and reaches completionat 24 h. Complexes of Â«2M-dgAcannot be dissociated by guanidine,sodium dodecyl sulfate, or low pi I, but can be partially dissociated byreducing agents, such as 2-mercaptoethanol in the presence of sodiumdodecyl sulfate. This indicates that dgA or dgA-containing immunotoxinsare bound to a2M by disulfide bonds. The dgA-binding site on a2M andthe mechanism underlying its interaction with dgA are different fromthose described for proteases or methylamine. 2Mcomplexes do notbind to Blue-Sepharose 4B or anti-A chain-Sepharose, suggesting thatthe sites on dgA which bind Cibacron Blue or polyclonal anti-A chainantibodies are sterically blocked or modified by interaction with,. 2M.The interaction of a2M with dgA or its immunotoxins results in a 2- to3-fold decrease in the activity of the dgA in both cell-free assays andcytotoxic assays. However 12 h after injection into mice, only 11% ofimmunotoxin was bound to Â«2Mbecause of the slow kinetics of theinteraction versus the more rapid r1/2 of the immunotoxin in thecirculation.
|Original language||English (US)|
|Number of pages||6|
|State||Published - Mar 1991|
ASJC Scopus subject areas
- Cancer Research