May 1, 1976

Purine catabolism in man: characterization of placental microsomal 5'-nucleotidase

Canadian Journal of Biochemistry
I H Fox, P J Marchant


Human placental microsomal 5'-nucleotidase (EC was prepared free of alkaline phosphatase by isoelectric focusing. A total of seven electrophoretic variants were isolated during the preparation of six placentas. Only three to six variants were found in a single placenta. The isoelectric pH's were 6.70, 6.44, 6.23, 6.02, 5.76, 5.63 and 5.44. These were found to be composed of variable quantities of a large, medium and low molecular weight form. The apparent molecular weights of the medium and light form of the enzyme were 86 500 and 43 500, respectively, as estimated from Stokes radius and sedimentation velocity determinations. The electrophoretic variants were not distinguishable with respect to specific activity and Michaelis constants for AMP, GMP or CMP or inhibition by ATP, CTP or adenosine. These electrophoretic variants appeared to be pseudoisozymes based upon different states of aggregation of a common primary sequence. There was a wide range of substrate specificity among nucleoside 5'-monophosphates which included 2-deoxyribose compounds. With AMP as 100, substrate activity was: CMP, 122; NMN, 74; GMP, 68: IMP, 63; XMP, 28 and UDP-glucose, 68. The Michaelis constants for AMP, GMP and CMP ranged from 12-18 muM, ...Continue Reading

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Mentioned in this Paper

Cations, Divalent
Structure-Activity Relationship
Purine Nucleotides
Hydrogen-Ion Concentration

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