Betaine-homocysteine methyltransferase (BHMT) catalyzes the remethylation of homocysteine. BHMT2 encodes a protein 73% identical in amino acid sequence to BHMT, but the function of BHMT2 remains unclear. We set out to identify and functionally characterize common genetic variation in BHMT and BHMT2. Specifically, we sequenced exons, exon-intron splice junctions and the 5′-flanking regions (5′-FRs) of BHMT and BHMT2 using 240 DNA samples from four ethnic groups. Twenty-five single nucleotide polymorphisms (SNPs), including 4 nonsynonymous SNPs, and 39 SNPs, including 4 nonsynonymous, were observed in BHMT and BHMT2, respectively. BHMT wild type (WT) and variant allozymes were expressed in COS-1 cells. Variant allozymes showed no significant differences from WT in levels of enzyme activity or immunoreactive protein, but there were statistically significant differences in apparent K m values. Luciferase reporter gene constructs were created for the three most common BHMT 5′-FR haplotypes, and significant variation was observed in the ability of these constructs to drive transcription. Although BHMT2 mRNA has been observed in human liver and kidney, expression of the protein has not been reported. We were unable to express BHMT2 in mammalian cells, and the protein aggregated after bacterial expression. Furthermore, BHMT2 was rapidly degraded in a rabbit reticulocyte lysate, but it could be stabilized by cotransfection of COS-1 cells with BHMT and, after cotransfection, it coprecipitated with BHMT. These studies have defined common genetic variation in BHMT and BHMT2 and functionally characterized BHMT SNPs. They may also help to explain why BHMT2 has not previously been defined functionally.

No abstract

The authors describe a colorimetric approach for on-site monitoring of histamine based on the use of gold nanoparticles (AuNPs) that have a negatively charged surface due to the presence of adsorbed citrate ions. Histamine has two basic functional groups, an aliphatic amino group and an imidazole ring. Under the experimental conditions, the protonated aliphatic amino group drives the imidazole ring into close proximity to the AuNPs due to electrostatic attraction. This accelerates the replacement of citrate ions by the imidazole ring because of the strong affinity between imidazole and AuNPs. As a consequence, the two groups synergistically induce the aggregation of the AuNPs and trigger a visible color change from red to blue. The minimum visually detectable histamine concentration is 1.81 μM, which is comparable to the limit of detection (LOD) of the electrochemical approaches at a signal-to-noise ratio of 3:1. When using absorbance at 522 nm, the LOD is lowered to 38 nM. The method was applied to the determination of histamine in fish samples.

No abstract

No abstract