The M_• − σ relation for galaxies at the high mass range (filled circles) and the first globular clusters with potential black hole detection (filled stars). The slope of the line log (M_•/M_⊙) = α + β   log (σ/200   km s^-1) with (α,β) = (8.12 ± 0.08,4.24 ± 0.41) was taken from Gültekin et al. (2009). The mass of the black holes of ω Centauri, G1 and the upper limits of M15 and 47 Tuc were obtained by Noyola et al. (2010), Gebhardt et al. (2005), van den Bosch et al. (2006) and McLaughlin et al. (2006), respectively. Overplotted is the result of NGC 6388 with our derived effective velocity dispersion σ_e = 18.9 km s^-1.