Why Should Tryptones Rather Than Bovine Serum Albumin Be Used as Model Proteins to Explore the Interactions between Proteins and Pollutants in Environments?

Because protein is readily degraded in the environment, it is unknown whether "protein-like substances" in environments are a group of intact proteins or a mixture of peptides and even amino acids. In this work, the widely adopted model protein bovine serum albumin (BSA) was compared with tryptones, an assortment of peptides, to evaluate their similarity with the proteins extracted from environmental samples. First, the physicochemical properties of BSA, tryptones, and the protein-like substances from the environmental samples were characterized, and the environmental protein-like substances and tryptones were found to have more aromatic groups than BSA and to be more unstable than BSA. Then, the interaction between proteins and metal ions or humic acids (HA) was examined. Differing from all of the other proteins, only the mixtures with BSA exhibited more significant fluorescence quenching and more positive specific ultraviolet-visible absorbance after interactions. Also, after binding to metal ions or HA, BSA tended to aggregate, while tryptones and the environmental protein-like substances did not. These results reveal that the environmental protein-like substances are more similar to tryptones than the model protein, BSA. Our work implies that tryptones, rather than BSA, should be a more appropriate alternative model in the investigation of protein-pollutant interactions.