Isolation of a Novel Viscous Protein from the Egg Mass of Japanese Sandfish (Arctoscopus japonicas)

Abstract

　In the ovaries of mature Japanese sandfish (Arctoscopus japonicas), eggs are enveloped by a jelly-like mucilage to form an egg mass. In a part of Japan, the sandfish egg mass is regarded as a delicacy due to its unique texture. Here, we successfully isolated the mucilage from the egg mass by soaking it in hot water at 70℃. The freeze-dried mucilage was comprised of 72% protein, 1.4% carbohydrate, and 21% crude ash. Because removal of the ash by dialysis did not alter the viscosity of the mucilage, the stickiness was attributed to the protein content of the mucilage. The viscosity of the mucilage was not stable at high temperatures, but the heat stability was improved by the presence of 1～5% NaCl. Interestingly, electrophoretic analysis indicated that the mucilage contains a single predominant protein. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis indicated that the protein had an oligomeric structure, which might result in the viscosity of the mucilage. The N-terminal amino acid sequence of the protein was determined to be NH₂-GRRGDRERNQ, which matched neither to known viscous proteins nor to known proteins in fish species. Consequently, the characteristic viscosity of the sandfish egg mass might be attributed to a novel viscous protein.