Abstract
Extract: The genetic variant of glucose phosphate isomerase (GPI) with hereditary nonspherocytic hemolytie anemia (GPI-Nordhorn) is purified 20,000-fold in a one-step procedure with a yield of 25%. A specific activity of about 100 IU per mg protein is obtained. The isoelectric point of the variant enzyme is 9.80, which is slightly higher than normal. The molecular weight is 94,000. Kinetic studies with the isolated enzyme gave results which are comparable to normal: Km (glucose 6-phosphate (G-6-P)) = 660 μM, Km (fructose 6-phosphate (F-6-P)) = 97 μM, Ki 6-phosphogluconate (6-PG) (G-6-P) = 43 μM, Ki 6-PG (F-6-P) = 19 μM, Ki 2,3-diphosphoglycerate (2,3-DPG) (F-6-P) = 850 μM, pH optimum (G-6-P) = 8.0, and pH optimum (F-6-P) = 8.5. It can be assumed that a genetically determined amino acid substitution causes the alteration of isoelectric point, electrophoretic migration, and increased thermolability but does not affect the active site of the enzyme.
Speculation: By the preparation of an enzyme variant reported herein a possibility is presented to obtain further structural characteristics by means of fingerprinting and amino acid analysis. It might be possible to correlate functional peculiarities to the altered structural properties of variant enzymes.
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Arnold, H., Blume, K., Löhr, G. et al. Glucose Phosphate Isomerase Deficiency with Congenital Nonspherocytic Hemolytie Anemia: A New Variant (Type Nordhorn). II. Purification and Biochemical Properties of the Defective Enzyme. Pediatr Res 8, 26–30 (1974). https://doi.org/10.1203/00006450-197401000-00005
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DOI: https://doi.org/10.1203/00006450-197401000-00005
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