Stickiness to hydrophobic surfaces varies widely among peptides and proteins.

To determine whether there are differences in stickiness to hydrophobic surfaces among peptides and proteins under immunoassay conditions, peptides and proteins were radio-labeled with (125)I and competitive adsorption with human serum albumin (HSA) in polystyrene or polypropylene tubes was used to determine the IC (50), the concentration of HSA required to reduce the adsorption of the labeled polypeptides to 50% of maximal. Stickiness was defined as log(10)(10(9) IC (50)). Stickiness varied significantly between the labeled polypeptides (p < 0.00001) and ranged (±sem) from 0.99 ± 0.07 for angiotensin II to 5.30 ± 0.07 for tyr(0)-urocortin II. The stickiness of HSA and γ globulin was 1.62 ± 0.09 and 1.92 ± 0.05, respectively. No significant difference in stickiness between polystyrene and polypropylene was found. We conclude that some peptides are sufficiently sticky to risk adsorptive loss during sampling and analysis, and there may exist peptides so sticky that they remain uncharacterized.