Effect of age on kinetics and carbon monoxide binding to cytochrome oxidase in synaptic and non-synaptic brain mitochondria

Abstract

The kinetic parameters of cytochrome oxidase activity in synaptic and non-synaptic brain mitochondria from 3- and 30-month-old rats were determined at room temperature. The value of K m for cytochrome c increased only 12–13% with age. The maximal velocity did not change with age, but the value of V max in synaptic mitochondria is twice that observed in non-synaptic mitochondrial cytochrome oxidase. The kinetics of CO binding to cytochrome oxidase at temperatures from 183 to 225K were also studied in synaptic and non-synaptic mitochondria from 3- and 30-month-old rat forebrains. Age-dependent differences were observed only in mitochondria of synaptic origin. Following flash photolysis at low temperatures, CO migration to the iron requires crossing two free energy barriers separating two intermediate regions from the iron. In 3-month-old synaptic mitochondria, CO must migrate across a 10.3 kca/mol barrier separating two intermedite regions, I 2 and I; a 4.7 kcal/mol barrier separates the innermost region I from the iron. Each intermediate region in 3-month-old cytochrome oxidase can hold only one CO molecule. In 30-month-old synaptic mitochondria, 10.3 kcal/mol barriers separate the two intermediate regions as well as region I and the iron; each intermediate region can hold two CO molecules. Region I 2 in non-synaptic cytochrome oxidase at either age can hold two CO molecules and the innermost region I holds only one CO molecule; energy barriers of approximately 10.3 kcal/moIe separate regions I 2, I, and the iron. These age-dependent changes may reflect age-dependent conformational changes in cytochrome oxidase.