ISSN:
1432-1327
Keywords:
Metalloenzyme
;
Binding constant
;
Binding stoichiometry
;
Nickel
;
Titanium citrate
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Clostridium thermoaceticum were determined by equilibrium dialysis. CoA bound to as-isolated native α 2 β 2 enzyme with K D = 10 ± 8 μM and n = 0.2 ± 0.1 moles per αβ dimer, where K D is the thermodynamic dissociation constant and n is the number of CoAs bound per αβ dimer of the enzyme. The enzyme is heterogeneous; for example, only ∼ 30% of α subunits contain A-clusters with labile Ni ions (the remainder have nonlabile Ni ions and are nonfunctional). The observed n value suggests that CoA binds only to αβ units with Ni-labile A-clusters. The CoA binding properties of enzyme lacking labile Ni was essentially the same, indicating that CoA does not bind directly to the Ni of the A-cluster. This was further evidenced by the observation that bound CoA did not inhibit removal of the labile Ni by 1,10-phenanthroline. CoA did not bind CO-reduced enzyme, and the EPR signal exhibited by the one-electron reduced and CO-bound form of the A-cluster was unaffected by the presence of up to 200 μM CoA. In contrast, CoA did bind Ti(III)-citrate-reduced enzyme (K D = 36 ± 16 μM, n = 0.16 ± 0.08). Implications of these results for the mechanism of catalysis are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050346
Permalink