Complex sentence: Receptor types I and II have similar ligand binding affinities and can only be distinguished from each other by peptide mapping, both receptor types I and II have a high affinity for TGF-β1 and low affinity for TGF-β2.
Split into simpler sentences: Receptor types I and II have similar ligand-binding affinities and can be distinguished from each other only by peptide mapping. Both receptor types I and II have a high affinity for TGF-β1 and low affinity for TGF-β2.