JBC, Vol. 252, Issue 15, 5183-5185, Aug, 1977
A novel nuclear relaxation approach for estimating distance between enzyme- and nucleotide-bound metal ions at the catalytic site of pyruvate kinase
R. K. Gupta
This communication introduces a nuclear relaxation approach for an
estimation of the distance between two paramagnetic metal ion sites on a
metal-activated enzyme. The method is based on the existence of an exchange
of unpaired electron spin magnetizations between the two metals via
energy-conserving concerted mutual spin flips which arise from
time-dependent dipolar interactions of the electronic magnetizations. This
cross-relaxation of electronic magnetizations depends on the inverse sixth
power of the intermetal distance and may, under suitable conditions, affect
the longitudinal relaxation rate of inner sphere water protons by altering
the electron-proton dipolar correlation time when the latter is dominated
by electron spin relaxation. The technique is applied to estimate the
distance of 5.2 +/- 0.9 A between Mn2+ and Cr3+ in the pyruvate
kinase-Mn2+-ATPCr3+ complex and indicates the existence of a van der Waals
contact between the hydration spheres of the enzyme- and nucleotide-bound
metal ions.
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