N-acetyl-galactosamine-specific lectin, a novel lectin in the haemolymph of the ascidian Halocynthia roretzi: isolation, characterization and comparison with galactose-specific lectin

Deformation Control and Mass Transfer in the Tunic of Halocynthia roretzi

Background:

It has been previously reported that the tunic ofHalocynthia roretzi, mainly composed of cellulose, is actively deformed with mass transfer by the mechanical stimuli.

Objective:

In this study, how the tunic deforms in response to the mechanical environment was investigated.

Method:

The tunic specimen in the artificial seawater was still at 5˚C or underwent the mechanical stimuli at the temperature less than 10˚C. The mass and moisture content of the tunic, the concentrations of nitrate and dissolved organic matter in the artificial seawater used for the tunic, and the histological characteristics were evaluated.

Results:

The increase in mass of the tunic became lower as the region was closer to the bottom ofHalocynthia roretzi. However, the decrease in mass caused by the mechanical stimuli was not different between the adjacent regions. Also, the tunic of the siphon, the tubular tissue for influx and efflux of the seawater, increased the mass more slowly after the stimuli. The size of the layer covering the outside of the tunic was inversely related to the increment in mass. The change in mass was corresponding to that in water content. The concentrations of nitrate and dissolved organic matter in the artificial seawater were enhanced 5 days after the stimuli while the concentration ratio of dissolved organic matter to nitrate was kept constant.

Conclusion:

The water content in the tunic was used for controlling the mass response to the mechanical environment.

Characterization of novel metallo-proteases released from ascidian hemocytes by treatment with calcium ionophore

We have previously demonstrated that calcium ionophore induced the release of a novel metallo-protease from hemocytes of a solitary ascidian, Halocynthia roretzi. Here, we isolated the enzymes, PI and PII, from the culture media of H. roretzi hemocytes, which had been treated with calcium ionophore, A23187. The purification procedure included hydrophobic and anion-exchange chromatographies, and gel filtration. The molecular weights of the enzymes were estimated to be 11,000 by gel filtration, but the apparent sedimentation coefficients were 5.0 S, which suggests that the H. roretzi enzymes are of larger proteins with molecular weights of 80,000-90,000. The most susceptible substrate was succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide, and the optimum pH was 8.0, in either case of PI or PII. The activities of PI and PII enzymes were strongly inhibited by metal-chelating agents and propioxatin A, but not by phosphoramidon, a typical metallo-protease inhibitor. Zinc and calcium ions were found to be essential for the maximum expression of protease activity in both enzymes. Thus, the isolated enzymes are characterized as phosphoramidon-insensitive metallo-proteases, which are inhibited by propioxatin A. Extracellular roles of these enzymes were also discussed.