Abstract

Pearl and nacre (mother of pearl) have similar chemical compositions. However, more than 20 proteins have been identified in nacre, yet none have been detected in pearl thus far. This study aimed to detect and identify protein in pearl. Two batches of pearls formed in Hyriopsis cumingii (Lea) were purchased from two pearl farms. They were ground into a powder of >10,000 mesh followed by ultra-sonication and extraction in water for 4 h at room temperature. The solution was centrifuged and the supernatant was saved as pearl powder water extract. A portion of the extract was heated at 121°C for 20 min. TCA precipitation and tricine–SDS-PAGE were conducted on both the heated and non-heated extracts. After silver nitrate staining, the heated extract demonstrated a distinct protein signal, but the non-heated extract did not. The protein band from each of the two heated extracts was excised from the gel and subjected to tryptic digestion and RP-nano-HPLC-ESI-MS/MS analysis. A MASCOT search of the results indicated that one protein had significant sequence homology to a putative vitelline envelop receptor for lysine in the common marine mussel Mytilus edulis, and the other to the putative imaginal disc growth factor (IDGF) of Diaprepes abbreviatus.

Key words: Pearl, nacre, Hyriopsis cumingii (Lea), RP-nano-HPLC-ESI-MS/MS analysis, MASCOT search, vitelline envelop receptor for lysine, imaginal disc growth factor.