| Yellowfin tuna (Thunnus albacares) muscle is subject to a form of deterioration known in the commercial market as burnt tuna. Because this condition substantially reduces the retail value of the tuna, its' prevention is important to the fishing industry. Previous work on burnt tuna suggested that it was caused by a calcium-activated neutral protease, calpain, that produced a limited proteolysis of the non-contractile myofibrillar proteins.; This dissertation research was divided into two parts. The first part constructed a working cellular definition of the whole animal condition identified as burnt tuna. Cellular differences in burnt tuna were quantified microanatomically and biochemically. Anatomical studies indicated a significant loss of Z-disc integrity and increase in intra-cellular edema in burnt tuna. In biochemical analysis, burnt tuna had a significant loss of a couplet of proteins, 46kD and 42kD. Both studies indicated that burnt tuna is a specific and limited proteolysis of myofibrillar structure.; The second part tested a theory that burnt tuna was caused by calpain, activated due to an increase in intracellular (ICF) Ca{dollar}sp{lcub}++{rcub}{dollar}, and accelerated by circulating catecholamines (CA). Isolated myofibrils incubated in purified calpain had proteolysis of the 46kD and 42kD proteins as well as limited proteolysis of other myofibrillar proteins. This occurred at all three pH's tested, 5.5, 6.8 and 7.5. Whole cell incubations of yellowfin tuna muscle in Ca{dollar}sp{lcub}++{rcub}{dollar} or EDTA buffered saline resulted in a generalized, non-specific proteolysis of myofibrillar proteins. This happened at each pH tested, 5.5, 6.8 and 7.5. Plasma epinephrine (E) and norepinephrine (NE) concentrations in disturbed yellowfin tuna were determined by HPLC to be.22{dollar}mu{dollar}g/ml and.48{dollar}mu{dollar}g/ml, respectively. Pre-treatment of the incubated whole cells with the beta-agonist, isoproterenol, did not induce a more specific proteolysis of the 46kD and 42kD proteins. Instead, a more rapid, generalized proteolysis occurred in cells incubated in Ca{dollar}sp{lcub}++{rcub}{dollar} or EDTA buffered saline.; Some exploratory experiments using either a metabolic stimulator, pyrophosphate (PPi), or a metabolic inhibitor, iodoacetate (IAA), suggest that the proteolysis occurring during the whole cell incubations is related to the quantity of glycogen present in the cell. A revised theory of burnt tuna is presented to provide a possible explanation for these exploratory results and to direct future research. |
