Vitamin K1 [HRP]

The electrochemical behaviour of vitamin K-1 (VK1) incorporated in a self-assembled monolayer of dioleoylphosphatidylcholine (DOPC) deposited on a hanging mercury drop electrode was investigated by a computerized chronocoulometric technique. The kinetics of VK1 electroreduction to the corresponding quinol, VK1H(2), and that of VK1H(2) reoxidation to VK1 were examined for reactant concentrations ranging from 0.5 to 2 mol% by varying the pH from 5.5 to 9 with phosphate and berate buffers. On the basis of a general kinetic approach it was concluded that the reduction of VK1 to VK1H(2) in a DOPC monolayer takes place via the reversible uptake of one electron, yielding the semiquinone radical anion VK1(.-), followed by the rate determining protonation of the latter. On the other hand, the oxidation of VK1H(2) to VK1 takes place via the reversible release of one electron, yielding the semiquinone radical cation VK1H(2)(+.), followed by the rate determining deprotonation of the latter. The only effective proton donors in VK1 reduction are the protons, whereas the main proton accepters in VK1H(2) oxidation are the water molecules. (C) 1998 Elsevier Science S.A. All rights reserved.

Faecal vitamin K1 (VK1, phylloquinone) and vitamin K2 (menaquinone, MK) concentrations were measured in 12 breast fed and 9 formula fed 1-month-old infants. Faecal concentrations of VK1 and MK-5 to -9 were significantly higher in the formula fed than in the breast fed infants. There was also a tendency for higher total faecal MK (4-10) concentrations in the formula fed [geometric mean (95% confidence intervals); 8995.0 (3872.6, 20893.0) pmol/g of dry faeces] than in the breast fed infants [2937.7 (1285.3, 6714.3), P = 0.051]. The numbers of streptococci and Escherichia coli were 100 and 10 times higher, respectively, in the faeces of the formula fed than in those of the breast fed infants. Faecal concentrations of MK-6, -7 and -8, and MK-8 were correlated with the numbers of streptococci and E. coli in the faeces, respectively. Serum VK1 and MK concentrations were measured in 9 out of 12 breast fed and eight out of nine formula fed infants. The serum VK1 concentration was much higher in the formula fed infants [average (95% CI); 2.20 (1.48, 2.92) pmol/ml] than in the breast fed ones [0.30 (-0.10, 0.70), P = 0.000], but MKs were not detected in the sera of most of the formula fed infants.