Cooperativity of thymopoietin 32–36 (the active site) and thymopoietin 38–45 in receptor binding

Abstract

Thymopoietin is a 49 amino acid polypeptide hormone of the thymus whose biological activity is reproduced by the synthetic pentapeptide thymopentin, corresponding to amino acids 32–36. Thymopentin requires the addition of an octapeptide corresponding to thymopoietin 38–45 for full competition with native thymopoietin in a radioreceptor assay with receptor derived from the human T-cell line CEM. Thus thymopoietin appears to bind to its receptor on T-cells by two regions (32–36 and 38–45). Thymopentin alone is biologically active and induces elevations of intracellular cyclic GMP. Whilst occupancy of the adjacent site by thymopoietin 37–45 does not of itself cause an elevation of intracellular cyclic GMP this peptide is not biologically silent as it does enhance the potency of thymopentin.