摘要:

ABSTRACTPolyphenol oxidase (EC 1.14.18.1) has been purified from Jerusalem artichoke tubers by immobilized copper affinity chromatography. The enzyme is primarily an o‐dihydroxyphenol oxidase with apparent Kmvalues of 1.9, 3.5 and 3.9 mM for chlorogenic acid, 4‐methylcatechol, and catechol, respectively. Several compounds exhibited inhibitory action for the enzyme in the order of: sodium metabisulfite>sodium diethyldithiocarbamate>2,3‐naphthalenediol>thioglycollate. Multiple forms were identified by gel filtration and SDS‐gradient polyacrylamide gel electrophoresis: two aggregates with apparent MW of 120 and 86 K and two monomeric subnits of 40–42 and 32–34 K, respectively. Concentration dependent association‐dissociation phenomena most likely determine the multimeric state of this enzyme. While the aggregated forms exhibited specificity towards mono‐, di‐ and polyhydroxyphenols, the low MW subunits were found active only with o‐dihydroxyphenols. The isoelectric points of the various enzyme species were within the range of 4.0 to 10.0. The enzyme was found to contain appreciable amounts of associated ca

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00133.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTAn acidic fraction of polyphenol oxidase (EC 1.14.18.1), representing the bulk activity, has been isolated from Jerusalem artichoke tubers by copper affinity chromatography, followed by DEAE‐Sepharose ion‐exchange chromatography. Isoelectric focusing analysis showed a cluster of activity bands (microheterogeneity) in the pH region of 4.5. The amino acid composition of the enzyme was also determined. The pH optimum for oxidation of chlorogenic acid, 4‐methylcatechol and catechol was 6.0. Substrate inhibition was observed by high concentrations of chlorogenic acid. Thermal inactivation data indicated an apparent activation energy of 26.2 kcal/mol. Kinetics of inactivation, upon copper removal by KCN treatment, and reconstitution reactions revealed that the former is a much slower process than reactiv

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00134.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTPotato tubers had 1.67% N/dry matter. Nitrogen was distributed in all anatomical regions of the tuber. Of the total N content, 43% was dialyzable‐N and 32.9% true protein‐N. The protein, by solubility fractionation, provided 67% albumin, 23% globulin, 1.4% prolamin and 9% glutelins. As revealed by sodium dodecyl sulfate electrophoresis (SDS‐PAGE), the albumin had two major protein species, one of 45 × 103, the second of 12–25 × 103daltons. Prolamin and glutelins contained protein bands coinciding in molecular weight with those of albumin and globulin.Protein hydrolysis with 4 N methanesulfonic acid was superior to that of 6 N HCL. Amino acid composition of proteins was determined by ion‐exchange column chromatography. Some minor losses in protein composition of potatoes occurred during

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00135.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTProtein synthesis inhibitors (Actinomycin D and cycloheximide) were infiltrated into banana slices by contact or under vacuum. Drastic reduction of the climacteric period was observed in both types of infiltration when cycloheximide was infiltrated into slices, compared to the Actinomycin D group and to a control group infiltrated with water. Ethylene production was stimulated when both protein synthesis inhibitors were used, in comparison to the water control group irrespective of the type of infiltration adopted. Ethylene production was higher in the vacuum infiltrated groups. It is suggested that cycloheximide and Actinomycin D affect the equilibrium of ripening differently, giving rise to the distinct responses observed.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00136.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTThe solubilization of proteins in corn and sorghum, using sodium lauryl sulfate (NaLS) in a basic medium, was used for tryptophan determination. The experimental design evaluated different levels of sodium lauryl sulfate and sodium hydroxide, at various temperatures and times. Prior to treatment, the samples were dried, ground and defatted. These were hydrolyzed and tryptophan was quantified spectrophotometrically (λmax= 565 nm). Casein was used as control and DL‐tryptophan was used for generating the standard curve according to Beer's Law. From the results obtained, it was possible to conclude that sodium lauryl sulfate was very effective in solubilizing corn and sorghum protein for subsequent tryptophan determinati

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00137.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Book Reviews in this article.Food Emulsions and Foams.Edited by E. Dickenson.Chemical Aspects of Food Enzymes. Edited by A.T. Andrews.Silent Spring Revisited.Edited by Gino J. Marco, Robert M. Hollingworth, and William Durham.Umami: A Basic Taste, Edited by Y. Kawamura and M.R. Kare.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00138.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00139.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1988.tb00132.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY