Abstract
In Euglena gracilis arginine deiminase was located in the mitochondrial matrix. The highly purified enzyme required Co2+ for the enzyme reaction with the Km value of 0.23mM, and its optimum pH was 9.7 to 10.3. The molecular weight of the native enzyme protein was 87, 000 by gel filtration, and SDS-acrylamide gel electrophoresis showed that the enzyme consisted of two identical subunits with a molecular weight of 48, 000. Euglena arginine deiminase was inhibited by sulfhydryl inhibitors, indicating that a sulfhydryl group is involved in the active center of the enzyme. It exhibited negative cooperativity in binding with arginine. L-α-amino-β-guanidinopropionate, D-arginine, and L-homoarginine strongly inhibited the enzyme while β-guanidinopropionate, γ-guanidinobutyrate, and guanidinosuccinate did not. Considerable inhibition was also observed with citrulline and ornithine. Wediscuss the effects of the unique properties of the Euglena arginine deiminase on the regulation of arginine metabolism in this protozoon.
