The immunoregulatory polypeptide prothymosin α and its biologically active N-terminal fragment thymosin α1m, with relative molecular masses of 12 500 and 3108 respectively, were found to behave as oligomers (trimers to hexamers) in gel-filtration measurements. This phenomenon of an apparent association of polypeptides has been reported for other thymosins — parathymosin α, thymosin β4 and thymosin β10. In contrast, sedimentation equilibrium ultracentrifugation shows that thymosin α1 is a monomer with a relative molecular mass of 3000±200. Measurement of the diffusion coefficient as 221 μm2/s suggests that the molecule is approximately spherical. The implications for the molecular species of prothymosin α, parathymosin α, and β-thymosins are discussed.
