[Physicochemical characteristics of salusin-beta and establishment of the radioimmunoassay].

Salusin-beta is a 20 amino acid bioactive peptide originally identified using bioinformatic analyses of human full-length enriched cDNA library. Salusin-beta has been shown to exert potent hypotensive, bradycardic, and pro-atherosclerotic effects. The form in which it exists in biological fluids remained undetermined due to technical difficulties originating from its unexpected physicochemical properties. Salusin-beta peptide adheres to polypropylene, glass and polystyrene, so that the aliquoted peptide dissolved in distilled water may rapidly disappear from the dissolved solution. Strategies to circumvent such problems in biological experiments include use of low doses of NP-40 or Tween-20 which alleviates its adhesiveness. Addition of 0.1% of NP-40 to the radioimmunoassay buffer markedly reduced non-specific binding of both labeled and unlabeled salusin-beta to the assay tubes without interfering the binding of salusin-beta to its antibody. Successful establishment of a specific radioimmunoassay suitable for detection of immunoreactive human salusin-beta allowed to characterize the molecular form of salusin-beta released from a human-derived cultured cell line.