Trimethylamine synthesis from cloline by oral microflora
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The nutrient choline, (a quaternary amine), is a major component of the normal diet in humans. Trimethylamine (TMA) and/or Dimethylamine (DMA), the degradation product(s) of choline formed by certain bacteria, are precursors of the chemical carciinogen nitrosodimethylamine (NDMA). The present experiments were aimed at studying the degradation of choline to TMA by bacteria in the human oral cavity. In our pilot experiments, mixed salivary bacteria] populations and clinical dental plaque samples formed TMA from choline. Therefore, three sources of bacterial cultures (reference strains,fresh plaque and salivary isolates) derived initially from oral flora were screened for TMA-forming activity. Streptocapcus sanguis (SSI, a facultative anaerobe) was identified to be one of the most important TMA-forming organisms. The process of the degradation of choline to TMA by SSI was enzyme mediate, obeying Michaelis-Menten kinetics with a V [subscript] max. app.= 1683 ± 140 nmol/mg protein/hr, K subscript app.= 184 ± 58 [mu]m. This TMA forming enzyme of SSI was membrane bound (activity was present in the pellet fraction of extracts), and required a bound divalent metal cation (sensitive to EDTA); the activity of crude extract was eliminated by dialysis against water. The enzyme activity was maximal at pH 7.5 - 8.5. More TMA was produced under a nitrogen environment than that under an air environment at 37 degrees C, and the production was increased as the incubation temperature was elevated from 4 degrees C to 5O degrees C. This activity was inhibited by deanol, betaine aldehyde, hemicholinium-3, iedoacetate, semicarbazide and 2, 4-dinitrophenol, and was enhanced by sulfthydryl reducing agents (glutathione, 2-mercaptoethanol, DL-dithiothreitol) and sodium bisulphite. This system studied is similar to that previously described in anaerobic bacteria (Desulfovibrio desulfuricans, Clostridium). The effect of varying osmotic pressure on TMA production by SSI was investigated, TMA production was decreased as the osmolarity increased from 25 mM to lOO mM KPi buffer. TMA nitrosation, forming NDMA, occured in two experimental systems studied. NDMA was formed when TMA was incubated with nitric oxide (NO) with air present in an organic soIvent (dichloromethane), and when TMA was incubated with nitrite (NO subscript 2-) in phosphate buffered saline and frozen for 6 days.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Includes photographs.Thesis (D.N.Sc.)--Boston University, Henry M. Goldman School of Graduate Dentistry, 1989 (Nutritional Sciences)Bibliography : leaves 103-118.
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