CATABOLISM OF L-4-HYDROXYPROLINE IN TISSUES OF HYBRID STRIPED BASS Morone chrysops × M. saxatilis
L-4-Hydroxyproline (Hyp) is one of several bioactive factors to improve the growth of fish. Traditionally, it has been considered to have limited nutritional value, but is now recognized as a substrate for the synthesis for glycine in mammals. At present, little is known about Hyp utilization in fish species. Therefore, the present study was conducted with hybrid striped bass to investigate Hyp metabolism in various tissues. Slices of skeletal muscle, liver, proximal intestine, kidney, stomach, heart, spleen, gill and brain obtained from juvenile hybrid striped bass were incubated in 26 °C for 2 h in 1 ml oxygenated Krebs-Henseleit bicarbonate buffer (pH 7.4, with 5 mM D-glucose) containing 0, 0.5, 2 or 5 mM Hyp. After a period of 2 h incubation, 200 μl of 1.5M HClO4 was added into the incubation medium to stop the reaction, and the acidified solution was neutralized by 100 μl of 2M K2CO3. The extract was analyzed for amino acids using our HPLC method.
Results indicated that glycine was produced from Hyp by fish skeletal muscle, liver, intestine, heart, kidney, spleen, and stomach. Small amounts of aspartic acid, glutamate, serine, and glutamine were generated from Hyp from these tissues. In contrast, fish gill and brain had little or no ability to convert Hyp into any amino acids. Our findings provide a new metabolic pathway for utilization of collagen and Hyp by hybrid striped bass (carnivores).