Oxygen affinity terminal oxidases in soybean mitochondria

Respiration of mitochondria isolated from roots and cotyledons of soybean seedlings was monitored over the range of 0-6 μM oxygen, using oxyleghaemoglobin or oxymyoglobin as oxygen sources in a closed system. From the data obtained, apparent Km oxygen values of approximately 0.14 μM for cytochrome oxidase and 1.7 μM for the alternative oxidase were calculated. The results indicate that the alternative oxidase cannot operate under the microaerobic conditions thought to prevail in nitrogen-fixing root nodules