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Biochimica et Biophysica Acta (BBA) …, 1974
Human IMP dehydrogenase has been partially purified from placenta and characterized. The enzyme a... more Human IMP dehydrogenase has been partially purified from placenta and characterized. The enzyme activity is located in the cytosol. The Michaelis constants for IMP and NAD are 14 and 46/~M, respectively. In addition, the enzyme requires a monovalent cation for maximal activity and the apparent Km for K + is 17 mM. The purine ribonucleotides XMP, GMP, and AMP inhibit the enzyme in a manner which is competitive with respect to IMP. The Ki values are 30/~M, 100 #M, and 530 #M, respectively. The enzyme is also sensitive to inhibition to a lesser degree by pyrimidine ribonucleotides. The pharmacologic agents, 6-mercaptopurine ribonucleotide, allopurinol ribonucleotide and mycophenolic acid are also inhibitors of human IMP dehydrogenase. A kinetic analysis indicates an ordered sequential reaction mechanism in which IMP binds first and XMP is released last.
Journal of Clinical …, 1972
Inosinic acid dehydrogenase was evaluated in normal subjects and in patients with the Lesch-Nyhan... more Inosinic acid dehydrogenase was evaluated in normal subjects and in patients with the Lesch-Nyhan syndrome. A significant difference in activity was found between erythrocytes derived from normal controls (1.21±0.47 pmoles/hr per mg protein) and from 15 patients with the Lesch-Nyhan syndrome (6.72 ±6.23 pmoles/hr per mg protein). However, no difference in activity was demonstrable in muscle or leukocytes derived from normal and Lesch-Nyhan patients. The increased activity of inosinic acid dehydrogenase in erythrocytes from patients with the Lesch-Nyhan syndrome is due to stabilization of the enzyme in vivo as well as the absence of an inhibitor which is present in erythrocytes from normal subjects.
Biochimica et Biophysica Acta (BBA) …, 1974
Human IMP dehydrogenase has been partially purified from placenta and characterized. The enzyme a... more Human IMP dehydrogenase has been partially purified from placenta and characterized. The enzyme activity is located in the cytosol. The Michaelis constants for IMP and NAD are 14 and 46/~M, respectively. In addition, the enzyme requires a monovalent cation for maximal activity and the apparent Km for K + is 17 mM. The purine ribonucleotides XMP, GMP, and AMP inhibit the enzyme in a manner which is competitive with respect to IMP. The Ki values are 30/~M, 100 #M, and 530 #M, respectively. The enzyme is also sensitive to inhibition to a lesser degree by pyrimidine ribonucleotides. The pharmacologic agents, 6-mercaptopurine ribonucleotide, allopurinol ribonucleotide and mycophenolic acid are also inhibitors of human IMP dehydrogenase. A kinetic analysis indicates an ordered sequential reaction mechanism in which IMP binds first and XMP is released last.
Journal of Clinical …, 1972
Inosinic acid dehydrogenase was evaluated in normal subjects and in patients with the Lesch-Nyhan... more Inosinic acid dehydrogenase was evaluated in normal subjects and in patients with the Lesch-Nyhan syndrome. A significant difference in activity was found between erythrocytes derived from normal controls (1.21±0.47 pmoles/hr per mg protein) and from 15 patients with the Lesch-Nyhan syndrome (6.72 ±6.23 pmoles/hr per mg protein). However, no difference in activity was demonstrable in muscle or leukocytes derived from normal and Lesch-Nyhan patients. The increased activity of inosinic acid dehydrogenase in erythrocytes from patients with the Lesch-Nyhan syndrome is due to stabilization of the enzyme in vivo as well as the absence of an inhibitor which is present in erythrocytes from normal subjects.