Terminal phenylalanine and tyrosine biosynthesis of Microtetraspora glauca

Chorismate mutase and 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase of the methylotrophic actinomycete Amycolatopsis methanolica

Chorismate mutase (CM) and 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase (DS) are key regulatory enzymes in L-Phe and L-Tyr biosynthesis in Amycolatopsis methanolica. At least two CM proteins, CMIa and CMIb, are required for the single chorismate mutase activity in the wild type. Component CMIa (a homodimeric protein with 16-kDa subunits) was purified to homogeneity (2,717-fold) and kinetically characterized. The partially purified CMIb preparation obtained also contained the single DS (DSI) activity detectable in the wild type. The activities of CMIa and CMIb were inhibited by both L-Phe and L-Tyr. DSI activity was inhibited by L-Trp, L-Phe, and L-Tyr. A leaky L-Phe-requiring auxotroph, mutant strain GH141, grown under L-Phe limitation, possessed additional DS (DSII) and CM (CMII) activities. Synthesis of both CMII and DSII was repressed by L-Phe. An ortho-DL-fluorophenylalanine-resistant mutant of the wild type (strain oFPHE83) that had lost the sensitivity of DSII and CMII synthesis to L-Phe repression was isolated. DSII was partially purified (a 42-kDa protein); its activity was strongly inhibited by L-Tyr. CMII was purified to homogeneity (93.6 fold) and characterized as a homodimeric protein with 16-kDa subunits, completely insensitive to feedback inhibition by L-Phe and L-Tyr. The activity of CMII was activated by CMIb; the activity of CMII plus CMIb was again inhibited by L-Phe and L-Tyr. A tightly blocked L-Phe- plus L-Tyr-requiring derivative of mutant strain GH141, GH141-19, that had lost both CMIa and CMII activities was isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

Prephenate dehydratase of the actinomycete Amycolatopsis methanolica: purification and characterization of wild-type and deregulated mutant proteins

Prephenate dehydratase (PDT) is a key regulatory enzyme in L-phenylalanine biosynthesis in the Gram-positive bacterium Amycolatopsis methanolica. The PDT protein was purified to homogeneity (1957-fold) from wild-type cells with a final yield of 6.5%. It was characterized as a 150 kDa homotetrameric protein with a subunit size of 34 kDa. The first 35 N-terminal amino acids were identified, revealing highest similarity to the PDT proteins from Corynebacterium glutamicum and Bacillus subtilis. Kinetic studies showed that the A. methanolica PDT is allosterically inhibited by phenylalanine and activated by tyrosine. Phenylalanine caused an increase in the S0.5 for prephenate and a decrease in the Vmax. Tyrosine caused a decrease in the S0.5 for prephenate and an increase in the Vmax. Spontaneous o-fluoro- and p-fluoro-DL-phenylalanine-resistant mutants of A. methanolica were isolated. Kinetic studies with the partially purified PDT proteins of strains pFPhe32 and oFPhe84 showed that these mutant proteins had become (partly) insensitive to both phenylalanine inhibition and tyrosine activation.

Biosynthesis of l-Phenylalanine and l-Tyrosine in the Actinomycete Amycolatopsis methanolica

Auxotrophic mutants of the actinomycete Amycolatopsis methanolica requiring l-Phe or l-Tyr were isolated and identified as strains lacking prephenate dehydratase (strain GH71) or arogenate dehydrogenase (strain GH70), respectively. A. methanolica thus employs single pathways only for the biosynthesis of these aromatic amino acids. Anion-exchange chromatography of extracts revealed two peaks with Phe as well as Tyr aminotransferase (AT) activity (Phe/Tyr ATI and Phe/Tyr ATII) and three peaks with prephenate AT activity (Ppa ATI to Ppa ATIII). Phe/Tyr ATI and Ppa ATI coeluted and appear to function as the A. methanolica branched-chain amino acid AT. Ppa ATII probably functions as the aspartate AT. Mutant studies showed that Phe/Tyr ATII is the dominant AT in l-Phe biosynthesis and in l-Tyr catabolism but not in l-Tyr biosynthesis. Biochemical studies showed that Ppa ATIII is highly specific for prephenate and provided evidence that Ppa ATIII is the dominant AT in l-Tyr biosynthesis.

Purification and N-terminal amino-acid sequences of bacterial malate dehydrogenases from six actinomycetales strains and from Phenylobacterium immobile, strain E

Malate dehydrogenases from Streptosporangium roseum (DSM 43021), Planomonospora venezuelensis (DSM 43178), Microtetraspora glauca (ATCC 23057), Actinoplanes missouriensis (DSM 43046), Streptomyces atratus (ATCC 14046), Kibdelosporangium aridum (ATCC 39323), and from Phenylobacterium immobile, strain E (DSM 1986) were purified to homogeneity. The N-terminal amino-acid sequences were determined and compared with known prokaryotic and eukaryotic sequence data. The partial sequences from Actinomycetales enzymes include a string of amino acids which is also present in the N-terminal region of malate dehydrogenases from Thermus flavus and from mammalian cytoplasm.