Regulatory properties of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase isozymes from Candida maltosa

✍ Scribed by Dr. R. Bode; C. Melo; D. Birnbaum

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: English
• Weight: 531 KB
• Volume: 25
• Category: Article
• ISSN: 0233-111X
• DOI: 10.1002/jobm.3620250102

✦ Synopsis

The first step in the biosynthesis of aromatic amino acids by Candida maltosa was eatalysed by two isozymes of 3-deoxy-~-arabino-heptulosonate 7-phosphate (DAHP) synthase. The formation of which was constitutive. The phenylalanine-sensitive and the tyrosine-sensitive DAHP synthases were partially purified by hydroxylapatite chromatography and several properties of the separated isozymes were studied. Both enzymes showed a molecular weight of 90,000. The Km-values of the tyrosine-sensitive DAHP synthase were 0.20 mM for erythrose-4-phosphate (E-4-P) and 0.50 mm for phosphoenolpyruvate (PEP). Inhibition of this isozyme reaction by L-tyrosine was competitive with respect to E-4-P (Ki = 0.028 mM) and non-competitive with respect to PEP.

The Km-values of the phenylalanine-sensitive DAHP synthase were estimated to be 0.85 mM for E-4-P and 0.63 mm for PEP; a Ki of 0.097 mix was obtained for L-phenylalanine. A number of tyrosine and phenylalanine analogues and biosynthetic intermediates also inhibited the two isozyme reactions. For example, we observed a strong inhibitory effect of p-hydroxyphenylpyruvate on the tyrosine-sensitive DAHP synthase and of phenylpyruvate on the phenylalanine-sensitive isozyme. Prephenate and arogenate had a less pronounced effect on the phenylalanine-sensitive DAHP synthase.