The amino acid sequence of a biologically active polypeptide isolated from calf thymus, termed thymosin al, has been determined. Thymosin a, is a heat stable, highly acidic molecule composed of 28 amino acid residues. This peptide is one of several present in thymosin fraction 5 that may participate in the regulation, differentiation, and function of thymus-dependent lymphocytes (T cells). A nomenclature for the family of polypeptides present in thymosin fraction 5 is suggested.
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α‐9‐Fluorenylmethyloxycarbonyl (Fmoc) amino acids will be of advantage in solid phase peptide synthesis. The Fmoc‐group is quantitatively cleaved by mild base (piperidine). This permits the use of tert‐butyl‐type side chain blocking and of peptide‐to‐resin linkage cleavable by mild acidolysis. Side reactions arising from repetitive acid deprotection and final HF cleavage in contemporary solid phase synthesis are avoided. Fully bioactive and homogeneous dihydrosomatostatin was obtained in 53% overall yield.
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