ESSENTIAL ARGINYL RESIDUES IN Cu,Zn SUPEROXIDE DISMUTASE FROM SACCHAROMYCES CEREVISIAE

Cu,Zn superoxide dismutase from baker's yeast, Saccharomyces cerevisiae, is inactivated by either butanedione in borate buffer or phenylglyoxal. Inactivation by butanedione takes place only in the presence of borate, and butanedione-inactivation is reversed on removal of borate. Initial studies with phenylglyoxal suggested that inactivation is due to the modification of 0.5 arginyl residues per subunit, or 1.0 per active dimer, as determined by amino acid analysis after acid hydrolysis in 6 M-HCI. Subsequent studies revealed that this value is too low due to regeneration of free arginine during acid hydrolysis, and that inactiv~ition is actually due to modification of 1.0 arginyl residues per subunit. This latter value was determined by amino acid analysis after acid hydrolysis in the presence of thioglycolic acid, and confirmed by use of [14C]phenylglyoxal and by quantitative fluorescence analysis using 9,10-phenanthrenequinone. Contrary to the conclusions of a similar study on the bovine erythrocyte enzyme (MALINOWSKI and FRIDOVICH: Biochemistry, 18, 5909-5917 (1979)), the reactive arginine in the yeast enzyme appears to be essential for dismutase activity, since this enzyme can be > 99 % inactivated by treatment with phenylglyoxal.