摘要:

14CO2was applied to apples and bananas that were stored at various temperatures and the incorporation of14C into oxalacetate was determined. Apples that were susceptible to internal breakdown showed an initial decrease in incorporation as the storage temperature was reduced but incorporation then increased at temperatures below 10°C (Jonathan) or 5°C (Twenty Ounce). Apples that were not susceptible to breakdown (Delicious and Granny Smith) showed no incorporation at any temperature. Green bananas showed a minimum incorporation at 10°C but in ripe bananas, incorporation markedly increased at all temperatures less than 20°C. The respiration rate of the apple varieties at 20°C was found to be higher in fruit that were more susceptible to breakdown whereas at O°C the higher rates of respiration were from fruit less susceptible to the dis

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00182.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Red kidney bean contains more amylase inhibitor than do California white bean and cowpea while garbanzo bean and Westan and Westley lima beans do not contain inhibitor. Red kidney bean amylase inhibitor was purified to homogeneity by selective heat treatment (60°C) of a water extract at pH 4. 0, fractionation with ethanol and successive chromatography on DEAE‐ and CM‐cellulose chromatography. The inhibitor has an apparent molecular weight of 49,000 by Sephadex gel filtration and contains 8. 6% carbohydrate probably covalently linked via an amide linkage to asparagine. The inhibitor probably contains four subunits perhaps of three different types. The inhibitor is high in aspartic acid, glutamic acid, serine, threonine and valine, low in cysteine/cystine and does not contain proline. Stable 1:1 complex formation between inhibitor and porcine pancreatic α‐amylase was demonstrated by gel filtration on Sephadex G‐100. The inhibitor has activity against porcine pancreatic α‐amylase, human salivary α‐amylase, and Tenebrio molitor (yellow corn meal worm) larval midgut α‐amylase but is inactive against Bacillus subtilis α‐amylase, Aspergillus oryzae α‐amylase, barley α‐amylase an

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00183.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α‐amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 104M‐1sec‐1at pH 6.9 (ionic strength of 0.918) and 2.55 × 105M‐1sec‐1at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme‐inhibitor complex was determined to be 3.5 × 10‐11M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10‐8sec‐1under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 104M‐1sec‐1at 370and 9.77 × 102M‐1sec‐1at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate‐controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α‐amylase, bound as readily to the enzyme‐inhibitor complex as to free α‐amylase. Trypsinized α‐amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibi

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00184.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Lactase, papain and lipase enzymes were immobilized concomitantly on derivatized Sepharose 4‐B. Equal molar concentrations of each enzyme were allowed to react with activated Sepharose and a preferential binding of lipase and papain over lactase was observed. This preferential binding was explained by differences in diffusion rates of enzymes resulting in greater availability of binding sites within the beads to certain enzyme species.The effects of pH of assay, temperature of assay and substrate concentrations on each individual enzyme were determined. Soluble forms of each enzyme were used for comparison. There were some differences in pH and temperature optima for the immobilized enzymes. However, the affinity of the enzymes for their substrates was substantially the sam

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00185.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Temporary anoxia created by submerging potato tubers in water completely inhibited light‐induced greening and glycoalkaloid formation of Russet Burbank, White Rose and Pontiac cultivar. Preanoxia vacuum treatment of the tuber has the same effect but hastened rottenness of the tubers. Anoxia treatment also inhibited the respiration of potato tissue. Partial exposure of the surface of anoxia tubers to air reduced the inhibition. The inhibition of the light‐induced greening by anoxia condition was due to inhibition of tuber respiration. The light absorption by the water used to create anoxia condition did not contribute to the inhibition of light‐induced greening. The duration which tubers could tolerate anoxia condition depended upon the cultivar and the physical condition of the tubers. Incorporation of 100 to 1000 ppm sodium hypochlorite or daily replacing with fresh water effectively improved incubation stability and reduced rotte

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00186.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Tyrosine phenol‐lyase catalyzes the conversion of L‐tyrosine to phenol, pyruvate, and ammonia. The activation energy for the reaction was calculated to be 13,000 calories per mole. The heavy metal Cu++was found to result in a mixed type of inhibition (Ki 0.20 mM). The addition of mercaptoethanol was found to reverse the inhibition by Cu++. Competitive inhibition was found with the amino acids L‐alanine (Ki18 mM) and L‐phenylalanine (Ki 4.4 mM). Phenol, an end product of the tyrosine phenol‐lyase reaction, was also found to inhibit enzyme activity (Ki 50 mM). Tyrosine phenol lyase catalyzed the formation of pyruvate from L‐tyrosine methyl ester, S‐methyl‐L‐cysteine, and L‐serine but at rates lower than with L‐tyrosine. Km values for L‐tyrosine methyl ester, S‐methyl‐L‐cysteine, and L‐serine were found to be 0.37 mM, 0.40 mM, and 1.2 mM, respectively. The reverse reaction by which L‐tyrosine is produced from phenol, pyruvate, and ammonia was demonstrated. The pH optimum for the reverse reaction was found to be

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00187.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

An endopolygalacturonase has been purified from a crude commercial preparation that is derived from cultures of Aspergillus niger. The polygalacturonase has a pH optimum of 4.5 and is relatively heat labile, losing activity when heated to 45°C. The purified preparation acts on the α‐1, 4‐galacturonosyl linkages present in polygalacturonic acid. It does not act on linkages present in a variety of substrates which contain virtually all of the glycosidic bond types described for the cell walls of monocots, dicots, and various f

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00188.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Book Reviews in this article.Handbook of Enzymatic Methods of Analysis. George G. Guilbault.Principles of Food Chemistry, John M. deMan.Laboratory Manual in Food Chemistry. A. E. Woods and L. W. Aurand.Advances in Enzymology, Vol. 44. Alton Meister, Editor.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1978.tb00189.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY