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It is considered the quasi-stationary approximation of a dynamic model, representing a positive feedback mechanism in the MEK/ERK signaling pathway mediated by RKIP. An analytical solution of the eight dimensional quasi-stationary system is found. Analytical relations between stationary and initial values of all signal pathway components are derived too. On the basis of them it is established that the quasi-stationary behaviour of a MEK/ERK pathway is dependent only on reactions of association and dissociation of the double phosphorylated protein ERKpp and the protein complex RKIP/Raf-1 to the three-component complex ERKpp/RKIP/Raf-1 and vice versa. Moreover, the leading role of initial concentrations of the RKIP protein complexes is determined.