  We study diffusion of particles on the surface of a sphere toward a partially
reactive circular target with partly reversible binding kinetics. We solve the
coupled diffusion-reaction equations and obtain the exact expressions for the
time-dependent concentration of particles and the total diffusive flux.
Explicit asymptotic formulas are derived in the small target limit. This study
reveals the strong effects of reversible binding kinetics onto
diffusion-mediated reactions that may be relevant for many biochemical
reactions on cell membranes.
