PRESSURE AND LACTATE-DEHYDROGENASE FUNCTION IN DIVING MAMMALS AND BIRDS

Emperor penguins (Aptenodytes forster), elephant seals (Mirounga angustirostris), and sperm whales (Physeter catodon) have been shown to dive to considerable depths (265 m, 1,500 m, and 1,140 m, respectively). These animals must cope with extreme changes in hydrostatic pressure as they dive. The effects of hydrostatic pressure on the Michaelis-Menten constant, K(m), of cofactor binding of NADH of muscle M4 (muscle type) lactate dehydrogenase (LDH) was measured for these diving vertebrates and compared with a nondiving mammal, the domestic rabbit. No effect of pressure changes as great as 2.066 X 10(4) kPa (204 atm) was observed in either the diving or nondiving species LDH preparations. Results support the hypothesis that, at least concerning the K(m) of NADH in the M4 LDH of the diving vertebrates examined, the LDHs of warm-blooded divers do not appear to be affected by changes in hydrostatic preSSure and the enzyme may be preadapted for insensitivity to pressure perturbations.