On the mechanism of divalent metal ion chelator induced activation of the 7S nerve growth factor esteropeptidase. Thermodynamics and kinetics of activation.

The 7S nerve growth factor protein (7S NGF) is a multisubunit zinc metalloprotein containing a masked trypsin-like esteropeptidase activity. Reaction of the native 7S NGF oligomer with divalent metal ion chelators effects an approximately sevenfold activation of the esteropeptidase activity via the sequestering and dissociation of the 7S NGF-bound zinc ion (Pattison, S. E., and Dunn, M. F. (1975), Biochemistry 14, 2733; Pattison, S. E., and Dunn, M. F. (1976), Biochemistry, preceding paper in this issue). In this study, investigation of the relationship between chelator concentration and the extent of activation, as measured by the steady-state rate of hydrolysis of alpha-N-benzoyl-D,L-arginine-p-nitroanilide, has demonstrated that (a) the chelator-induced activation is a freely reversible process, (b) activated 7S NGF undergoes a slow loss of reversibility when incubated with chelator over long time-periods, (c) the affinity constant of 7S NGF for zinc ion is approximately 10(10.5) +/- 10(0.5) M(-1), (d) chelator activation depends only on the ability of the chelator to sequester zinc ion, and (e) the activation process does not involve dissociation of the 7S oligomer to smaller subunit aggregates under conditions of low ionic strength.