Reaction of nerve growth factor gamma and 7S nerve growth factor complex with human and murine alpha 2-macroglobulin

The kallikrein-like serine proteinase nerve growth factor gamma (NGF-gamma) reacted with the plasma proteinase inhibitor human alpha 2-macroglobulin (h alpha 2M). The h alpha 2M subunits were cleaved, the electrophoretic mobility of h alpha 2M in nondenaturing polyacrylamide gels was increased, and the intrinsic fluorescence of h alpha 2M was increased with a slight blue-shift. These changes are well-characterized components of the alpha 2M/proteinase reaction mechanism. In N alpha-benzoyl-DL-arginine p-nitroanilide (BAPNA) hydrolysis experiments, the catalytic efficiency (kcat/KM) of the h alpha 2M-NGF-gamma complex was decreased by 98.5% compared with free NGF-gamma. This decrease is unique since other alpha 2M-proteinase complexes retain significant amidase activity. For comparison, we determined that the catalytic efficiency of alpha 2M-trypsin is decreased by 58% compared with free trypsin under equivalent conditions. The rate of NGF-gamma inhibition by h alpha 2M was (1.0 +/- 0.1) x 10(4) M-1 s-1 as determined by BAPNA hydrolysis. A similar value was determined by monitoring the change in intrinsic fluorescence. NGF-gamma, which was bound within the intact 7S NGF complex, also reacted with h alpha 2M, albeit at a very slow rate. This reaction may have depended exclusively on slow reversible dissociation of NGF-gamma from the 7S complex. NGF-gamma was rapidly inhibited by murine alpha 2M (m alpha 2M).(ABSTRACT TRUNCATED AT 250 WORDS)