Many mutagenic heterocyclic amines (HAs) have been isolated from cooked foods and pyrolysates of amino acids and proteins, and the carcinogenicity of 10 of these HAs in rodents and of 1 in monkeys has been reported. Quantification of these carcinogenic HAs in various kinds of cooked foods indicated that the level of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was highest (0.56-69.2 ng/g), that of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was second highest (0.64-6.44 ng/g), and those of other HAs were 0.03-2.50 ng/g. Heterocyclic amines were found in urine samples of 10 healthy volunteers consuming a normal diet, but HAs were not detectable in urine samples of three patients receiving parenteral alimentation. These results strongly suggest that humans are continuously exposed to HAs derived from food in the normal diet. Based on quantitative data on the levels of HAs in cooked foods and urine samples, the daily exposures to PhIP and MeIQx were estimated to be 0.1-13.8 micrograms and 0.2-2.6 micrograms per person, respectively. These levels of carcinogenic HAs are in the same range as those of other carcinogens such as N-nitrosodimethylamine and benzo[a]pyrene to which humans are exposed.
Chondroitin sulphate (ChS) from the scapular cartilage of the shortfin mako shark (Isurus oxyrinchus) was purified by two-stage enzymatic hydrolysis and a fractional precipitation process using isopropyl alcohol. Characteristics of the ChS fraction were investigated using cellulose acetate membrane electrophoresis and FT-IR spectra. A maximum hydrolysis rate of 78.26% was achieved with 1.35% (w ⁄ w) Alcalase and 1.20% (w ⁄ w) Flavourzyme. A minimum nitrogen content of 2.89% was obtained with 1.43% (w ⁄ w) Alcalase and 1.33% (w ⁄ w) Flavourzyme, as determined by response surface methodology. The precipitation of ChS from the enzymatic hydrolysates was optimised at 40% (v ⁄ v) isopropyl alcohol, which contained 2% (w ⁄ v) NaCl to lower the nitrogen content. The precipitate was further purified via membrane filtration (molecular-weight cut-off, 3 kDa) to remove salt and low-molecular-weight materials. The ChS purified by enzymatic hydrolysis, isopropyl alcohol precipitation and membrane filtration was identified as ChS C by electrophoresis and FT-IR spectra.
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