METABOLIC RESPONSE TO OXYGEN LIMITATION IN ARENICOLA-MARINA AS DETERMINED WITH THE H-1-NMR SIGNALS OF MYOGLOBIN

During hypoxic stress many intertidal animals preserve their functiona l integrity by down regulating their energy utilization and by compens ating the aerobic energy loss with anaerobic ATP production. Arenicola marina is a well established invertebrate model in which aerobic meta bolism starts to decline well above the critical oxygen point. Even th ough the A. marina oxygen consumption profile versus ambient O-2 is we ll characterized, the underlying biochemical mechanism regulating intr acellular oxygen metabolism in vivo remains unclear. Recently,H- 1 NMR has opened an approach to observe tissue oxygenation with the signals of myoglobin (Mb). The deoxy Mb proximal histidyl NdeltaH and the oxy Mb valine Ell gamma CH3 signals are detectable in tissue and along wi th the Mb p(O-2)(50), can yield a quantitative measurement of the intr acellular oxygen level. The A. marina Mb proximal histidly NdeltaH sig nals appear at 93.4 and 92.5 ppm (25 degrees C), respectively, while t he corresponding valine Ell gamma CH3 signals appear at - 2.83 and - 2 .74 ppm. As the p(O-2) declines, MbO(2) saturation and MVO2 decrease. However, phosphotaurocyamine concentration remains unaltered until the MbO(2) saturation falls below 33%. The data suggest that the critical intracellular p(O-2) value is below 0.1 kPa (1 torr). The study estab lishes the H-1 NMR technique as an approach to measure the intracellul ar p(O-2) with an oxygenated state marker and presents the interrelati onship between oxygen and the metabolic adaptation during hypoxic stre ss. (C) 1998 Elsevier Science Inc. All rights reserved.