VITAMINS

Show abstractHide abstract

Since assessment of human vitamin E status from a clinical standpoint has generally relied on plasma tocopherol concentrations, which are recently recog-nized to be easily influenced by the plasma lipid concentrations, the evaluation on vitamin E nutrition seems to be yet confused. This paper has reported that RBC tocopherol levels may be useful for the nutritional assessment of vitamin E status in clinical practice, since RBC tocopherol depends on the nutritional status of vitamin E. First, tocopherol in RBCs was confirmed to be able to protect the membrane stability from various oxidant stresses, such as superoxide and hydroperoxide radicals generating systems. Then, it was estimated that changes in RBC tocopherol concentrations generally reflect the changes of tocopherol concentra-tions in effective sites of tissues, as the nutritional state of vitamin E was changed in rats. In humans, plasma tocopherol concentrations increased with age, while RBC tocopherol concentrations were almost constant throughout life in the population study in children and adults. Then, the lowest normal range of RBC tocopherol levels was arbitrarily estimated as 115 μg/dl packed cell volume on the cumulative percentage frequency from the population. On the basis of RBC tocopherol concentrations, premature infants with more than 1,500g birth weight revealed no vitamin E deficiency immediately after birth and throughout the neonatal life. Even in the very low birth weight premature infants, especially with less than 1,000g birth weight, normal tocopherol concentration in RBCs were also observed immediately after birth, which however decreased below the normal range during the first 4 to 7 weeks of life, probably due to their impaired absorption of fat including vitamin E. It was further observed that hyperlipemia and adiposity lowered RBC tocopherol concentrations. Under the conditions representing a lowered RBC tocopherol, a decrease in tocopherol concentrations may develop in intracellular components.

View full abstract

Download PDF (1562K)

Nicotinate methyltransferase (EC 2.1.1.7) was purified from marine clam by ammonium sulfate fractionation (60-90% sat.) and aflinity chromatography (nicotinic acid coupled AH-Sepharose 4B column). The final enzyme preparation was not stable. Properties of the enzyme was investigated with a stable ammonium sulfate fraction of marine clam. Principal results obtained were as follows: optimum pH for the reaction, 6.0; stable pH range for storage, 6-8; Km value for nicotinic acid, 4.0 μM; Km value for S-adenosyl-L-methionine, 3.2 μM; optimum temperature for the reaction, 36℃; activation energy, 20,460 cal/mol; inhibitors, heavy metal ions, PCMB, picolinic acid and isonicotinic acid (competitive inhibitors, each Ki=0.1 mM), nicotinamide (noncompetitive inhibitor, Ki=8.6 mM, hence this enzyme preparation was clearly different from nicotinamide methyltransferase), trigonelline (product inhibition); reverse reaction, not detectable. Consequently, it was suggested that the biosynthesis of trigonelline in marine clam may be regulated by picolinic acid, nicotinamide, trigonelline concentration, etc.

View full abstract

Register with J-STAGE for free!