Production of 2-Methylisocitric Acid from n-Paraffins by Mutants of Candida lipolytica |
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Authors: | Takeshi Tabuchi Seigo Hara |
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Affiliation: | Faculty of Agriculture, Tokyo University of Education, Komaba, Meguro-ku, Tokyo |
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Abstract: | Vitamin B12-dependent ribonucleotide reductase purified from Rhizobium meliloti catalyzes the reduction of 5′-diphosphates of guanosine, adenosine, cytidine and uridine (GDP, ADP, CDP and UDP). The enzyme activities were regulated by Mg2+ and deoxyribonucleoside triphosphate effectors as follows: in the presence of Mg2+, allosteric effector deoxyguanosine triphosphate (dGTP) had the most stimulatory effect on reduction of ADP and UDP; deoxyadenosine triphosphate (dATP) on reduction of CDP; and thymidine triphosphate (dTTP) on reduction of GDP. These stimulatory effectors were active at a low concentration of 10 μm. Other deoxyribonucleotides may be negative or weakly positive effectors. Without effectors, the rate profile of ADP and GDP reduction showed a sigmoidal curve. In the absence of Mg2+, the activities of the reductase showed nearly maximal levels, and the addition of effectors rather decreased the activities, except in the case of UDP reduction which was most strongly stimulated by dGTP. The effect of Mg2+ can be replaced by Ca2+. Monovalent cations such as Na+ and K+ had a negligible effect on the activities of ribonucleotide reductase. |
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