Complex sentence: The later class of complexes are made up of "alpha" (α), "beta" (β) and "gamma" (γ) subunits, the latter two form a stable dimeric complex referred to as the beta-gamma complex.
Split into simpler sentences: The later class of complexes are made up of "alpha" (α), "beta" (β) and "gamma" (γ) subunits. In addition, the beta and gamma subunits can form a stable dimeric complex referred to as the beta-gamma complex.