白血病細胞におけるIMP脱水素酵素  [in Japanese] IMP dehydrogenase in human leukemic cells  [in Japanese]

Access this Article

Author(s)

    • 後藤 治子 GOTO Haruko
    • 愛知県心身障害者コロニー発達障害研究所 Institute for Developmental Research, Aichi Prefectural Colony
    • 棗田 豊 NATSUMEDA Yutaka
    • インディアナ大学医学部実験腫瘍学研究所 Laboratory for Experimental Oncology, Indiana University School of Medicine
    • WEBER George
    • Laboratory for Experimental Oncology, Indiana University School of Medicine

Abstract

急性骨髄性白血病(AML)患者の白血球中のイノシン(-5'-)-リン酸(IMP) 脱水素酵素,およびヒト培養Tリンパ芽球MOLT4Fより精製した酵素の酵素化学的性質と代謝阻害剤tiazofurinの細胞内活性体TAD(thiazole-4-carboxamide adenine dinucleotide)による阻害を比較検討した.Tiazofurinの効果がみられたAML患者の白血球中のIMP脱水素酵素活性(33.4±0.1nmol/h/mg protein)は正常白血球(3.1±0.5)に比べ約11倍に上昇していた.また培養細胞では赤血白血病由来のK562(47.6),Bリンパ性白血病由来のBALL1(61.0),Tリンパ性白血病由来のMOLT4F(45.7), いずれも高値を示した.AML患者の白血球中のIMP脱水素酵素のIMP,NADに対するKm値はそれぞれ,23,44μMで,キサントシン(-5'-)一リン酸(XMP)による阻害はIMPに競合的,NADHはIMP,NAD両者に混合型阻害を示した.TADの阻害はNADHと同じ形式をとったが, Ki値は0.10μMとNADH(150μM)に比べはるかに低く,高い親和性が認められた. MOLT4Fより精製した酵素はサブユニットの分子量が約6万,IMP,NADに対するKm値はそれぞれ,29,54μMで,XMP,NADH,TADによる阻害形式,およびKi値(XMP=85,NADH=94,TAD=0.08μM)もラット肝癌酵素やAML患者の白血球酵素と同様であった.これらの結果はtiazofurinがAMLのみならず,Tリンパ性白血病にも効力をもつことを示唆する.

We investigated the kinetic properties and the effects of thiazole -4- carboxamide adenine dinucleotide (TAD), an active metabolite of tiazofurin, on IMP dehydrogenase in leukocytes from acute myeloid leukemia (AML) patients and on the enzyme purified from MOLT 4F cells. IMP dehydrogenase activity in human leukemic cell extracts from AML patients (33.4±0.1nmol/h/mg protein) was 11-fold increased compared to normal leukocytes (3.1±0.5). Human cultured cell lines, K 562 (47.6), BALL 1 (61.0) and MOLT 4F (45.7), also had elevated activities. Km values for IMP and NAD of leukemic IMP dehydrogenase from AML patients were 22.7 and 44.0μM, respectively. XMP showed competitive inhibition with IMP and noncompetitive inhibition with NAD. NADH showed mixed type inhibition with both IMP and NAD. The inhibitory pattern of TAD was similar to that of NADH, but the affinity of TAD to the enzyme (Ki=0.10μM) was three orders of magnitude higher than NADH (Ki=150μM). IMP dehydrogenase purified from MOLT 4F cells had similar kinetic properties (Km for IMP=29; NADH=54μM) and inhibitory mechanisms by natural products (Ki for XMP=85; NADH=94μM) and by TAD (Ki=0.075μM), as the enzyme from AML patients. These results suggest the usefulness of tiazofurin in the treatment of not only AML but also lymphoid leukemia.

Journal

  • Purine and pyrimidine metabolism

    Purine and pyrimidine metabolism 13(2), 120-128, 1990

    Japanese Society of Gout and Nucleic Acid Metabolism

Codes

Page Top