Physical Aspects of Reversible Inactivation

Most early investigations of the chemistry of endotoxins were limited to gross analyses. I t soon became apparent that subtler means of degradation, such as enzymes, were necessary to determine structural configurations and intramolecular relationships within the endotoxin complex. Just such a subtle endotoxin-degrading system was suggested by the observation of Hegemann (1954) that human plasma factors inactivated the pyrogenic properties of endotoxin. The applicability of this reaction became particularly evident when further studies showed that smaller-sized antigenic units of endotoxin appeared to be produced during the plasma-endotoxin reaction (Rudbach and Johnson, 1961, 1962; Skarnes and Chedid, 1964). The kinetics of the endotoxin-altering reaction, measured by reduction in the pyrogenicity of endotoxin (Keene, Landy and Shear, 1961) and by reduction in ability of endotoxin to precipitate quantitatively with homologous antiserum (Stauch and Johnson, 1959), lent credence to the theory that a plasma enzyme was degrading the endotoxin polymer. This endotoxin-altering system was shown to be inhibited by divalent cations (Rosen et al., 1958) and by other plasma components (Yoshioka and Johnson, 1962). These and other observations (cf. Atkins, f960; Landy, 1960) supported the contention that a plasma enzyme was degrading the endotoxin polymer. However, proof of this must be the isolation of degraded products which have come from a previously intact endotoxin molecule. This evidence has not been presented to date. Furthermore, other evidence has indicated that endotoxin may not be cleaved by plasma hydrolases. Rudbach and Johnson (1964) demonstrated that, after alteration of endotoxin by plasma, activity could be restored by procedures not considered likely to reverse an enzymatic hydrolysis.