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The micronutrients folate and selenium may modulate DNA methylation patterns by affecting intracellular levels of the methyl donor S-adenosylmethionine (SAM) and/or the product of methylation reactions S-adenosylhomocysteine (SAH). WI-38 fibroblasts and FHC colon epithelial cells were cultured in the presence of two forms of folate or four forms of selenium at physiologically-relevant doses, and their effects on LINE-1 methylation, gene-specific CpG island (CGI) methylation and intracellular SAM:SAH were determined. At physiologically-relevant doses the forms of folate or selenium had no effect on LINE-1 or CGI methylation, nor on intracellular SAM:SAH. However the commercial cell culture media used for the selenium studies, containing supra-physiological concentrations of folic acid, induced LINE-1 hypomethylation, CGI hypermethylation and decreased intracellular SAM:SAH in both cell lines. We conclude that the exposure of normal human cells to supra-physiological folic acid concentrations present in commercial cell culture media perturbs the intracellular SAM:SAH ratio and induces aberrant DNA methylation.

Steady-state kinetic approaches were used to investigate the binding of a novel Penicillium funiculosum xylanase, XYNC, with three known xylanase inhibitor proteins from wheat ( Triticum aestivum ). The xylanase gene ( xynC ) was cloned from a P. funiculosum genomic library and the deduced amino acid sequence of XYNC exhibited high sequence similarity with fungal family 11 xylanases. xynC was overexpressed in P. funiculosum and the product (XYNC: M r =23.6 kDa; p I =3.7) purified and shown to efficiently degrade birchwood xylan [ K m =0.47% w/v, V max =2540 μmol xylose min (mg protein) at pH 5.5 and 30 °C] and soluble wheat arabinoxylans [ K m =1.45% w/v, V max =7190 μmol xylose min mg protein) at pH 5.5 and 30 °C]. The xylanase activity of XYNC was inhibited strongly by three xylanase inhibitor proteins from wheat; XIP-I, TAXI I and TAXI II. The inhibition for each was competitive, with very tight binding ( K i =3.4, 16 and 17 nM, respectively) equivalent to free energy changes (Δ G °) of −49, −45 and −45 kJ mol. This is the first report describing a xylanase that is inhibited by all three wheat xylanase inhibitor proteins described to date.

A domain of glucoamylase 1 from Aspergillus nigerwhich binds to granular starch was produced by proteolytic digestion and purified to apparent homogeneity by extraction with corn starch followed by anion-exchange chromatography and gel filtration. The peptide has a molecular weight of 25100, contains approximately 38% carbohydrate ( ww) and corresponds to residues 471–616 at the C-terminus of glucoamylase 1. The peptide bound to granular corn starch maximally at 1.08 nmolmgstarch. It inhibited the hydrolysis of granular starch by glucoamylase 1 but had no effect on the hydrolysis of starch in solution.

Unlabelled cadaverine did not diminish the incorporation into anabasine of 14C from L-[U-14C] lysine supplied to hairy root cultures of Nicotiana nesperis, despite causing a stimulation of anabasine production. The finding is discussed in the context of previous observations indicating that free cadaverine is not an intermediate in the biosynthesis of anabasine from lysine.