By P. Amcoff, G. Akerman, H. Borjeson, U. Tjarnlund, L. Norrgren, L. Balk
Marine Environmental Research, Volume 50, Issues 1-5, July 2000, Page 75, ISSN 0141-1136, DOI: 10.1016/S0141-1136(00)00154-9.

Since 1974, Baltic salmon, Salmo salar, alevins have been affected by the M74 syndrome, a putative thiamine deficiency with associated high mortality levels that may be reduced by thiamine treatment. This study demonstrates that alevins with M74 suffer from lowered activities of the thiamine-dependent enzymes transketolase and [alpha]-ketoglutarate dehydrogenase compared to control fish. In addition, cytochrome P4501A-activity (CYP1A; measured as EROD) is lower in M74-affected alevins. Thiamine treatments administered after hatching resulted in increased activities of transketolase, [alpha]-ketoglutarate dehydrogenase and CYP1A in the M74 groups, restoring the thiamine-dependent enzyme activities to levels comparable to those of controls. We suggest that low activities of transketolase and [alpha]-ketoglutarate dehydrogenase may be responsible for M74-associated mortality. Low transketolase activities may reduce the intracellular availability of ribose 5-phosphate and NADPH. Ribose 5-phosphate is necessary for protein synthesis and NADPH is the cofactor for NADPH-cytochrome P450 reductase. Reduced cellular availability of these compounds may result in the reduced CYP1A-activities observed in this study.

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