Using identical Ga flux density, we have measured the growth rate difference between GaAs and GaSb. The large discrepancy of 15% seems to suggest a change in the sticking coefficient of Ga when different group V species are involved. However, when lattice parameters are taken into account correctly, the discrepancy appears to be a natural consequence because fewer Ga atoms are needed to complete a monolayer on the GaSb surface. Similar results are also observed for the growth of Al(Sb,As) and In(Sb,As). This points to the possible systematic error in the estimation of ternary composition, such as InGaAs, by adding the growth rates of binary constituents InAs and GaAs without correction for change in lattice constants.