Abstract
The molecular weight of quinolinate phosphoribosyltransferase from Aicatigenes eutrophus nov. subsp. quinolinicus (IAM 12305) was estimated by gel filtration and ultracentrifugation respectively to be about 210, 000 and 222, 000. The enzyme contains eight identical subunits with a molecular weight of 27, 500 each. Optimum pH (constant concentration) and isoelectric point were 8.5_??_9.0 and 5.3, respectively. Optimum temperature was 60°C. H2PO4-inhibited the activity. The enzyme activity was also inhibited by increase in ionic strength. At constant ionic strength, the maximum activity was obtained at pH 9.5. The kinetic data of the reaction are consistent with the formation of a ternary complex comprising the enzyme, quinolinic acid and 5-phosphoribosyl-l-pyrophosphate. Reaction product was identified as l-nicotinic acid mononucleotide.
