function J = eqljac(x,a,epsk,c)
% J = eqljac(x,a,epsk,c)
% 
% Jacobian of the enzyme kinetics equilibrium problem
% 
J = [ 1+c*x(3)/epsk     0         c*x(1)/epsk;
          0         1+x(3)/epsk^2   x(2)/epsk^2;
        c*x(3)/epsk   x(3)/epsk^2 (1+c*x(1)/epsk+x(2)/epsk^2)];