Abstract
Extract: Liver biopsy samples from the patients with hyperphenylalaninemia have an average of 5% of the normal hydroxylase activity. The parents of the patients have between 7.3% (excluding the value for one parent) and 10% of the normal hepatic hydroxylase activity. An explanation for these findings involves negative interallelic complementation, which involves protein-protein interaction between subunits in a multitneric enzyme. In support of this model is the evidence that rat liver phenylalanine hydroxylase is a multimeric protein composed of two electrophoretically distinguishable subunits.
Speculation: The finding that parents of patients with hyperphenylalaninemia have an average of 10% of the normal level of hepatic phenylalanine hydroxylase, a multimeric enzyme, can be explained on the assumption that the liver tissue of heterozygotes has an excess of enzyme molecules that contain at least one mutant subunit.
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Kaufman, S., Max, E. & Kang, E. Phenylalanine Hydroxylase Activity in Liver Biopsies from Hyperphenylalaninemia Heterozygotes: Deviation from Proportionality with Gene Dosage. Pediatr Res 9, 632–634 (1975). https://doi.org/10.1203/00006450-197508000-00004
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DOI: https://doi.org/10.1203/00006450-197508000-00004
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