DNA = 1;
DNA_A = 0;
DNA_B = 0;
DNA_A_B = 0;

A = 1;
B = 1;

kfA = 1;
krA = 1;
kfB = 1;
krB = 1;
kfB2AB = 1;
krB2AB = 1;
kfA2AB = 0.9;
krA2AB = 0.9;

DNA + A -> DNA_A,	kfA;
DNA_A -> DNA + A,	krA;
DNA + B -> DNA_B,	kfB;
DNA_B -> DNA + B,	krB;
DNA_B + A -> DNA_A_B,	kfB2AB;
DNA_A_B -> DNA_B + A,	krB2AB;
DNA_A + B -> DNA_A_B,	kfA2AB;
DNA_A_B -> DNA_A + B,	krA2AB;

A_bound = [(kfA/krA)*A];
B_bound = [(kfB/krB)*B];
AB_bound =[(kfA/krA)*(kfA2AB/krA2AB)*A*B];
Occ_Prom = [(AB_bound)/(1 + A_bound + B_bound + AB_bound)];