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

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Abstract
[The 7S growth factor protein (7S NGF) [from mouse submaxillary gland] is a multisubunit Zn metalloprotein containing a masked trypsin-like esteropeptidase activity. Reaction of the native 7S NGF oligomer with divalent metal ion chelators effects an approximately 7-fold activation of the esteropeptidase activity via the sequestering and dissociation of the 7S NGF-bound Zn ion]. 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-DL-arginine-p-nitroanilide, demonstrated: the chelator-induced activation is a freely reversible process; activated 7S NGF undergoes a slow loss of reversibility when incubated with chelator over long time-periods; the affinity constant of 7S NGF for Zn ion is .apprx. 1010.5 .+-. 100.5 M-1; chelator activation depends only on the ability of the chelator to sequester Zn ion; and the activation process does not involve dissociation of the 7S oligomer to smaller subunit aggregates under conditions of low ionic strength.

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