MICE WITHOUT MYOGLOBIN

Myoglobin, an intracellular haemoprotein expressed in the heart and ox idative skeletal myofibres of vertebrates, binds molecular oxygen and may facilitate oxygen transport from erythrocytes to mitochondria, the reby maintaining cellular respiration during periods of high physiolog ical demand(1-10). Here we show, however, that mice without myoglobin, generated by gene-knockout techhnology, are fertile and exhibit norma l exercise capacity and a normal ventilatory response to low oxygen le vels (hypoxia). Heart and soleus muscles from these animals are depigm ented, but function normally in standard assays of muscle performance in vitro across a range of work conditions and oxygen availability. Th ese data show that myoglobin is not required to meet the metabolic req uirements of pregnancy or exercise in a terrestrial mammal, and raise new questions about oxygen transport and metabolic regulation in worki ng muscles.