We present a set of,state of the art,large scale direct N-body simulations of the galaxy collision with the central Supermassive Black Hole system(SMBH).We use the maximum N = 1M particles to represent the colliding galaxies.The SMBH system is described using the two high mass special,such as “relativistic”,particles.The interaction between these two particles has an extra post-Newtonian correction terms(PN)up to 3.5PN level.Our results show that the so called “mass deficit” effect can reach up to the~30%level at the realistic galaxy-galaxy merging scenario(with galaxies mass ratio from 1/10 to 1/3).We also demonstrate that in a case of highly unequal mass galaxy mergers the BBHs merging time are significantly smaller compare to the equal mass galaxy merging case for the similar BH masses.