Abstract
Tissue-type transglutaminase (TGase: EC 2. 3. 2. 13) is a calcium-dependent enzyme that catalyzes the cross-linking and amine incorporation of proteins by an acyl transfer reaction. It is widely distributed in various tissues of fish and aquatic invertebrates, as well as mammals. The TGases from marine invertebrates such as bivalves and gastropods are strongly activated with NaCl and Ca2+ concentrations found in normal seawater. For example, the activity of scallop adductor muscle TGase increases 11-fold in 0.5M NaCl and 10mM CaCl2, while the activity of carp muscle enzyme is independent of salt concentration. Freshwater shellfish TGases are not activated with increased NaCl. These findings suggest that the physiological functions of marine invertebrate TGases are closely related to their surroundings. As marine bivalves and gastropods are osmoconformers and have an open blood-vascular system, their muscle cells are exposed to hemolymph that is isosmotic to seawater. When the muscle membrane is damaged by mechanical wounding or biochemical destruction, tissue TGase may be activated by contact with hemolymph and/or seawater, and thereby participate in the healing process.
