Takenori Takizawa

Publications (3)9.61 Total impact

• Article: Molecular basis of Japanese variants of pyrimidine 5'-nucleotidase deficiency.

  Hitoshi Kanno, Takenori Takizawa, Shiro Miwa, Hisaichi Fujii
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  ABSTRACT: The type-I isoform of pyrimidine 5'-nucleotidase (P5N-I) has an important role in the catabolism of pyrimidine mononucleotides during erythroid maturation. Two alternatively spliced forms of P5N-I mRNA have been identified, and we found another alternatively spliced form in reticulocytes, which included an additional 87-bp sequence. The sequence is located 6.2-kb downstream of the exon 2 and 2.7-kb upstream of the exon 3 sequence; consequently, the P5N-I gene encodes 11 exons, which span approximately 48 kb. We identified five novel mutations in nine families with P5N-I deficiency: two missense mutations (425C, 721C), one splice mutation (339C), one 1-bp insertion (251-insA-252) and one 9-bp deletion (del 192-200). All patients were homozygous for each mutation. The mutant P5N-I with 721C (G241R) had lower affinity for cytidine monophosphate, suggesting that Gly241 is important for substrate binding. Haplotype analysis showed that 721C, which had been identified in five unrelated families, was a founder mutation. The mutant P5N was then expressed in Cos-7. The degradation of P5N with 425C (L142P) was significantly faster than a wild-type control, and proteasome inhibitors restored the stability of L142P. These data suggest that L142P increases susceptibility to the degradation by the ubiquitin-proteasome pathway.
  British Journal of Haematology 08/2004; 126(2):265-71. · 4.94 Impact Factor
• Article: Red cell adenylate kinase deficiency associated with hereditary nonspherocytic hemolytic anemia: Clinical and biochemical studies

  Shiro Miwa MD Professor, Hisaichi Fujii, Kenzaburo Tani, Keisuke Takahashi, Takenori Takizawa, Takashi Igarashi, Shiro Miwa
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  ABSTRACT: We report here a case of red cell adenylate kinase (AK) deficiency associated with hereditary hemolytic anemia. The proband is a 10-year-old Japanese girl. Her physical and mental development was normal. She has shown moderate to mild hemolytic anemia since the neonatal period and hepatosplenomegaly. The red cell AK activity was 44% of normal. Contents of red cell glycolytic intermediates and adenine nucleotides were normal when compared with a comparable reticulocyte-rich control. Glucose consumption and lactate formation were normal. Hexose monophosphate shunt activity was somewhat lower than that of a comparable reticulocyte-rich control. There were no significant differences in the contents of adenine nucleotides between the younger and older red cells of the patient. Enzymatic characterization by hemolysate revealed that the patient's AK had an increased Michaelis constant for adenosine diphosphate and slight thermal instability. The patient's enzyme migrated approximately half-way between the AK 1 and AK 2 position on starch-gel electrophoresis. The mode of inheritance of this case is obscure. The mechanism of hemolysis might be a structural gene mutation that caused altered electrophoretic and kinetic properties.
  American Journal of Hematology 05/1983; 14(4):325 - 333. · 4.67 Impact Factor
• Article: A single nucleotide base transition is the basis of the common human glucose-6-phosphate dehydrogenase variant A(+)

  Takenori Takizawa, Yoshimasa Yoneyama, Shiro Miwa, Akira Yoshida
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  ABSTRACT: The X-chromosome-linked glucose-6-phosphate dehydrogenase (G6PD) A(+) is a common variant found in about 20% of blacks. The amino acid substitution of Asp in the variant G6PD A(+) for Asn in the normal G6PD B(+) was previously found (A. Yoshida, 1967, Proc. Natl. Acad. Sci. USA 57: 835), but the exact substitution position has not been identified. By screening a DNA library prepared from genomic DNA of a G6PD A(+) male subject, we obtained a genomic clone that contained the mutation site. Characterization of the clone revealed that transition occurred in the variant A(+) gene, thus producing the amino acid substitution Asn → Asp at the 142nd position from the NH2 terminus of the enzyme. The nucleotide change created an additional FolI cleavage site in the variant A(+) gene; thus, the FokI fragment type of the variant subjects differed from that of normal B(+) subjects in Southern blot hybridization analysis.
  Genomics.