(De)regulation of key enzyme steps in the shikimate pathway and phenylalanine-specific pathway of the actinomycete Amycolatopsis methanolica

Prephenate dehydratase (PDT), chorismate mutase (CM) and 3-deoxy-D-arabino-7-heptulosonate 7-phosphate (DAHP) synthase are key regulatory enzymes in aromatic amino acid biosynthesis in the actinomycete Amycolatopsis methanolica. Deregulated, feedback-control-resistant mutants were isolated by incubation of A. methanolica on glucose mineral agar containing the toxic analogue p-fluoro-DL-phenylalanine (pFPhe). Several of these mutants had completely lost PDT sensitivity to Phe inhibition and Tyr activation. Mutant characterization yielded new information about PDT amino acid residues involved in Phe and Tyr effector binding sites. A. methanolica wild-type cells grown on glucose mineral medium normally possess a bifunctional CM/DAHP synthase protein complex (with DS1, a plant-type DAHP synthase). The CM activity of this protein complex is feedback-inhibited by Tyr and Phe, while DS1 activity is mainly inhibited by Trp. Isolation of pFPhe-resistant mutants yielded two feedback-inhibition-resistant CM mutants. These were characterized as regulatory mutants, derepressed in (a) synthesis of CM, now occurring as an abundant, feedback-inhibition-resistant, separate protein, and (b) synthesis of an alternative DAHP synthase (DS2, an E. coli-type DAHP synthase), only inhibited by Tyr and Trp. DS1 and DS2 thus are well integrated in A. methanolica primary metabolism: DS1 and CM form a protein complex, which stimulates CM activity and renders it sensitive to feedback inhibition by Phe and Tyr. Synthesis of CM and DS2 proteins appears to be controlled co-ordinately, sensitive to Phe-mediated feedback repression.

Impaired prenatal and postnatal growth in Dutch patients with phenylketonuria. The National PKU Steering Committee.

OBJECTIVE--To assess whether physical growth is affected in early treated Dutch patients with phenylketonuria (PKU). METHODS--The birth weights of all 137 early detected patients with PKU born in the period from 1974 to 1988 in the Netherlands were compared with reference values. Height, head circumference, and weight were measured at the age at which treatment started (commonly about 2-3 weeks), at 6 months of age, and yearly from the child's first birthday up to the age of 10 years. These measurements were compared with reference values. RESULTS--The adjusted birth weight in patients with PKU was 141 g (95% confidence interval (CI) 66 to 216 g) less than Dutch reference values by Kloosterman and 103 g (95% CI 9 to 196 g) less compared with the birth weight of another reference group. At the age at which treatment started, z scores of patients for height by age were -0.23 (95% CI -0.44 to -0.02) and z scores for head circumference by the age were -0.25 (95% CI -0.44 to -0.06). From the age at which treatment started up to the age of 3 years z scores for height by age further decreased to -0.74 (95% confidence interval -0.93 to -0.56), after which no additional decrease occurred. In contrast, z scores for head circumference increased from -0.25 at the first visit to 0.08 (95% CI -0.14 to 0.30) at the age of 1 year, after which they remained close to zero. Weight by height was close to the expected centiles for all ages. CONCLUSION--Patients with PKU are growth retarded at birth and have smaller head circumferences than the normal population. In Dutch patients further growth retardation occurs in the first three years of life