Biochemical Properties of Water-Soluble Otolith Proteins and the Immunobiochemical Detection of the Proteins in Serum and Various Tissues in the Tilapia Oreochromis niloticus

Abstract

The water-soluble proteins (WSP) of otoliths were electrophoretically and immunochemically studied in the tilapia Oreochromis niloticus. WSP were separated into three or more undefined bands by gradient native PAGE and into 14-16 bands with a main band at 52 kDa by gradient SDS-PAGE. The main band was PAS-positive and had a moderate calcium-binding capacity. Proteins extracted from the sacculus showed an intense calcium-binding capacity in a single band in the low molecular region. Immunoelectrophoresis and immunoblotting revealed that anti-WSP rabbit serum was positive to the WSP, serum, and extracts from various tissues, including the sacculus, semicircular canal, heart, liver, gill lamella, and brain. These immunoreactions, except those of the WSP and the brain, disappeared after absorption with tilapia serum. Two-dimensional electrophoresis revealed that at least two serum proteins at 20 kDa and 21 kDa immunoreacted with the antiserum. The amino acid composition of the 20-kDa protein was dominated by Glx but was not necessarily similar to that reported for tilapia otoliths.