Complex sentence: In the heterotropic form it is only the effector that performs the role of modulation.at this junction the allosteric site of the enzyme could range from one (monovalent) or from two and above (polyvalent).
Split into simpler sentences: In the heterotropic form it is only the effector that performs the role of modulation. At this junction the allosteric site of the enzyme could range from one (monovalent) or from two and above (polyvalent).