IKUKO TOMINO

Publications (2)0 Total impact

• Article: Studies on Ornithine-Ketoacid Transaminase: I. Purification and Properties

  Nobuhiko KATUNUMA, Yoshiko Matsuda, IKUKO TOMINO
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  ABSTRACT: Ornithine-ketoacid transaminase was purified from rat liver mitochondria to an almost single protein on starch zone electrophoresis and ultracentrifugation pattern. The purified enzyme is 400-fold in the purity. Physico-chemical properties of the enzyme were studied and gave the following values; S 20, w ; 7.1 × 10−13 M , optimum pH; 8.2, K m for α-ketoglutarate 8.45×10−4 M , for ornithine; 6.0×10−4 M . Substrate specificity of the enzyme with respect to ketoacid was studied and the following reaction rates were observed, α-Ketoglutarate 100, glyoxalate 19, pyruvate 3 and oxaloacetate 0.7. The enzyme was found to require pyridoxal phosphate as the coenzyme. Canalline strongly inhibited the enzyme reaction. Oxaloacetate inhibited the reaction competitively with α-ketoglutarate. L-Valine, L-isoleucine and L-leucine were also found to be the inhibitors of the enzyme.
• Article: Regulation of glutaminase activity and differentiation of the isozyme during development

  Nobuhiko Katunuma, Tsunehiko Katsunuma, Ikuko Tomino, Yoshiko Matsuda
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  ABSTRACT: We purified phosphate-independent glutaminases in liver and kidney to homogeneous proteins. The mode of activation of kidney enzyme caused some allosteric transition other than polymerization by maleate and unknown compound purified from kidney. Liver PIG displayed a typical sigmoidal velocity curve with respect to the substrate concentration and the sigmoidal curve was converted to a normal curve in the presence of activators (N-acetyl glutamate or maleate). This result provides evidence that the enzyme is polymerized in the presence of the substrate and the activators facilitate the polymerization of the enzyme. These activations may play a significant role in regulation of organ-specific glutamine metabolism.The fetal liver contains both the liver and kidney type glutaminases and also fetal kidney contains both the kidney and liver type enzymes. The kidney type enzyme in fetal liver was decreased gradually after birth, disappearing completely within one week. No kidney type enzyme was found in the regenerating liver in spite of its rapidly growing nature. From this evidence we offered our working hypothesis on the differentiation of organ characteristic isozyme.
  Advances in Enzyme Regulation.