[Certain functional characteristics of enzymatic antioxidant defense in human blood plasma].

It has been shown that human blood plasma displays a low activity of superoxide dismutase, a key enzyme of antioxidative protection. This enzyme was isolated and purified from human blood plasma by using a novel procedure based on gel filtration on Ultrogels AcA-34 and AcA-44. Data from gel filtration and disc electrophoresis in the presence of sodium dodecyl sulfate and beta-mercaptoethanol suggest that the molecular mass of the enzyme decreased with time and a simultaneous change in activity. Purification of superoxide dismutase from blood plasma revealed the presence of low molecular mass peptides (1000 and 5000 Da) which inhibited the enzyme activity. A possibility was considered for superoxide dismutase transition into an active, conformationally labile state after a split-off of the inhibiting fragment under conditions of oxidative stress.