摘要:

ABSTRACTA variety of substances was evaluated for antioxidant or prooxidant activity in an aqueous model system of linoleic acid, Triton X‐100, and 2‐thiobarbituric acid solidified with agar in a Petri plate. Test samples were applied to wells cut from media. The oxidation reaction was initiated with ferric/ferrous chloride (50 mM/50 mM). Quantitative data were obtained by determining the diameter of the reaction ring surrounding test substance. Test substances and linoleic acid were oxidized, then subjected to the 2‐thiobarbituric acid (TBA) test for comparison. Simulated food systems were also tested using both systems. Correlation coefficients between the test method (inverse ring diameter, cm) and nmoles malondialdehyde/ml measured by the TBA test were r = 0.98, 0.90, and 0.91 for BHA, vitamins E and C, respect

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00857.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTβ‐Amylase inhibitors WKB 858B and WKB 858B were purified to homogeneity from different cultivars of white kidney beans by extraction from the ground beans and by sequential heat treatment, ethanol fractionation, DEAE‐cellulose chromatography, Sephadex G‐75 gel chromatography and CM‐cellulose chromatography. The inhibitors were homogeneous by 7.5% polyacrylamide gel electrophoresis; no isoinhibitors were found. Inhibitors WKB 858A and WKB 858B had isoelectric points of 5.0 and 4.65, respectively, and molecular weights of 42,000 and 20,000, respectively, by FPLC Superose 12 gel filtration chromatography. Inhibitor WKB 858A had molecular weights of 40,000 and 38,000 by Sephadex G‐75 gel filtration chromatography and by native gel electrophoresis, respectively. Inhibitor WKB 858A contained 11.0% carbohydrate, N‐linked to asparagine residues, with a composition of 1 fucose, 1 xylose, 4 galactose, 8 N‐acetylglycosamine and 13 mannose residues per mol of inhibitor. Amino acid analysis of Inhibitor WKB 858A gave a high content of Asx, Glx, Ser, Thr and Val (combined total of 60% molar ratio) and low content of sulfur amino acids (0.8% molar ratio of Met and no 1/2 cystine). No‐SH groups were found. The amino acid composition was similar to that of eight other a‐amylase inhibitors from beans. Inhibitor WKB 858A formed a 1:1 stoichiometric complex with porcine pancreatic a‐amylase with a Ki of 1.0 × 10−11M at pH 5.4 and 30C; it had no trypsin inhibitory activity. At pH 6.90 and 30C, the rate of complex formation between Inhibitor WKB 858A and porcine pancreatic β‐amylase was 2.76 times faster at 1.385 vs 0.035 ionic strength (with Na2SO4), indicating hydrophobic bonds are most impo

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00858.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTBoth white kidney bean α‐amylase inhibitors WKB 858A (MW 42,000) and WKB 858B (MW 20,000) were composed of two subunits as determined by N‐terminal amino acid analysis by amino acid sequence, by SDS‐PAGE and by separation on a chromatofocusing column in 8 M urea. N‐Terminal amino acids for Inhibitor WKB 858A were alanine and glycine, with a sequence of H2N‐Ala‐Glu‐Asn‐Ala‐Gly‐Thr‐Tyr–COOH for deglycosylated 9,000 MW peptide and H2N‐Gly‐Asn–COOH for deglycosylated 12,000 MW peptide. N‐Terminal amino acids for Inhibitor WKB 858B were alanine and serine, with a sequence of H2N‐Ala‐Thr‐Glu‐Thr‐Ser–COOH for the deglycosylated 9,000 MW peptide and H2N‐Ser‐Ala‐Val‐Gly‐Leu‐Asp‐Phe‐Val‐Leu‐Val‐Pro‐Val‐Gin‐Pro‐Glu‐Ser‐Lys‐Gly‐Asp‐Thr‐VaVal‐Glu‐Phe‐Asp–COOH for the deglycosylated 15,000 MW peptide. Chemical modification of 2 of 7 His residues with diethylpyrocarbonate resulted in 26% loss of inhibitory activity. Modification of 1.5 of 7 Trp residues with N‐bromosuccinimide gave 60% loss of inhibitory activity. Modification of 2 of 6 Tyr residues with N‐acetylimidazole gave 60% loss of inhibitory activity. Modification of 3.6 of 6 Arg residues with p‐hydroxyphenylglyoxal gave 64% loss of inhibitor activity. These results indicate the possible importance of one or more

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00859.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTArthrobotrys oligospora,when grown in synthetic medium with pectin as sole carbon source, produced pectin methylesterase (PME) on the fourth day under static conditions at 25C. Through ammonium sulfate fractionation and successive chromatography on hydroxyapatite and Sephadex G‐100 a 26.4 fold purification was achieved. PME was stable between pH values of 5–8. Its optimum activity was at pH 7.5 and at 37C. The energy of activation (Ea) was determined to be 11.9 kcal/mole. It had Kmof 0.9 mg/ml for pectin. The molecular weight of PME was found to be 50 kilo daltons by both Sephadex G‐100 column chromatography and by SDS‐PAGE. During electrophoresis PME appeared as a lipoprotein when prestained with sudan

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00860.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTBook reviewed in this article:FOOD INTOLERANCE. M.H. Lessof

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY