Not too big. Not too small. Because of their intermediate size, macrocyclic peptides combine the potency and precise targeting of an antibody or biologic therapy with the stability and ease of administration of a Intermediate Cu(II) Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction Inorganic Chemistry Tachyphylaxis an overview ScienceDirect Topics The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline