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Ascidian phenoloxidase: its release from hemocytes, isolation, characterization and physiological roles
1Department of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
Summary
The solitary ascidian Halocynthia roretzi releases phenoloxidase from hemocytes, a key enzyme in its immune defense. This metalloenzyme, crucial for antibacterial activity, plays a vital role in the ascidian
Area of Science:
- Marine biology
- Immunology
- Biochemistry
Background:
- The solitary ascidian Halocynthia roretzi possesses a unique immune system.
- Hemocytes are key cellular components involved in immune responses.
- Phenoloxidase is an enzyme implicated in invertebrate immunity.
Purpose of the Study:
- To investigate the release and characteristics of phenoloxidase from Halocynthia roretzi hemocytes.
- To determine the role of phenoloxidase in the defense mechanisms of H. roretzi.
Main Methods:
- Hemocyte isolation and stimulation with various agents (sheep red blood cells, yeast, zymosan, LPS).
- Enzyme purification using SP-Sephadex chromatography and Sephadex G-100 gel filtration.
- Characterization of enzyme activity, molecular weight, and cofactor requirements (copper ions).
Main Results:
- Hemocytes released phenoloxidase in response to microbial components (yeast, zymosan, LPS) but not inert particles (latex beads).
- Purified phenoloxidase had a molecular weight of 62,000 and was identified as a copper-dependent metalloenzyme.
- The enzyme exhibited antibacterial activity in the presence of specific substrates and plasma.
Conclusions:
- Phenoloxidase is released from H. roretzi hemocytes and functions as a humoral factor in the ascidian's defense system.
- The enzyme's activity is modulated by microbial stimuli and requires copper ions.
- This study elucidates the role of phenoloxidase in the innate immunity of H. roretzi.