Effect of aging on pulmonary superoxide dismutase.

Pulmonary Cu,Zn superoxide dismutase was examined in young (1-month-old), adult (4-5-month-old) and aged (24-months-old) rats to determine if partially inactive forms of the enzyme accumulate in the lung with age. Measurement of Cu,Zn superoxide dismutase activity in lung homogenates showed that total Cu,Zn superoxide dismutase activity/mg DNA was essentially the same in adult and aged rats. The average value of Cu,Zn superoxide dismutase/mg DNA for young rats was less than half that of adult and aged rats. Cu,Zn superoxide dismutase was purified from the lung homogenates and fractionated into isoelectric variants by either isoelectric focusing or chromatofocusing. Three main isoelectric variants of Cu,Zn superoxide dismutase were recovered with pI values of 5.15, 4.88 and 4.75. In all age groups studied, the pI 4.88 variant had a markedly higher specific activity than the other two variants, as well as the highest metal content and greatest resistance to inactivation of all three variants. The pI 4.88 variant declined from 88% of the total Cu,Zn superoxide dismutase activity in the young animals to only 70% in the aged animals. The results of this study indicate that the proportion of the relatively inactive forms of pulmonary Cu,Zn superoxide dismutase increased with age.