California Sea Grant College Program

The goal of this research is to investigate the biochemistry of solitary ascidians, with particular focus on the hemocytes (blood cells). Styela plicata and Ciona intestinalis have a high local abundance and their hemocytes are easily isolated, making them an appropriate model for histochemical studies. Because ascidian hemocytes mediate host defense reactions and accumulate specific metals, they are a potential source of novel antimicrobial and metal binding agents. Acid soluble peptides from ascidian hemocytes were investigated to determine their antimicrobial properties. Chapter II of this thesis presents a comprehensive review of marine invertebrate antimicrobial peptides. Chapter III describes the characterization of plicatamide, a modified octapeptide from hemocytes of the ascidian S. plicata. Chapter IV investigates the molecular origins of plicatamide and Chapter V describes attempts to generate a polyclonal antibody to plicatamide. Chapter VI presents, in detail, the antimicrobial properties of plicatamide. Chapter VII describes two novel, partially characterized, antimicrobial peptides from the ascidian C. intestinalis. Chapter VIII introduces a novel, potential metal binding agent from the acid extracts of S. plicata hemocytes. Appendix A reviews natural peptide antibiotics from tunicates and appendix B presents the unusual gas-phase intramolecular rearrangement of tunichrome Sp-1 presented in Chapter VIII.