Radiation Inactivation of Rabbit Muscle Aldolase

Abstract

Pulse radiolysis and steady-state X-radiolysis have been used to investigate the radiation inactivation of aldolase from rabbit muscle. Both e_aq⁻ and OH readily react with aldolase, and contribute to inactivation. The radical anions (CNS)₂⁻ and (Br)₂⁻ react with aldolase at neutral pH. The progressive addition of alkali results in an increase in the second-order rate constants, with an apparent pK ∼ 10 ± 0·3, and with the formation of an unstable intermediate, λ_max ∼400 nm resembling a phenoxyl radical. Steady-state radiolysis in the presence of (CNS)₂⁻ and (Br)₂⁻ at alkaline pH results in increased aldolase inactivation, with a pK of enzyme inactivation similar to that observed for reaction of the radical anions. We propose that a reaction of the radical anions with tyrosine residues accounts for the resultant inactivation.