摘要:

ABSTRACTStudies were carried out to determine the effects of cytosol on sarcoplasmic reticulum lipid peroxidation. Upon addition of unfractionated cytosol to the lipid peroxidation system, inhibition was observed. Fractionation revealed that both the low molecular weight (LMW) cytosol (6,000–8,000 MW) fractions inhibited lipid peroxidation. It is suggested that either inorganic phosphate compounds or nucleotides may be responsible for the LMW cytosol's inhibitory characteristics. Addition of the HMW cytosol fraction to the system necessitated the presence of additional adenosine 5′‐diphosphate (ADP) for optimal activity. ADP bound to the HMW cytosol fraction may be incapable of chelating the iron and preventing its precipitation as the ferric hydr

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTIn each of 5 tomato (Lycopersicon esculentum Mill) cultivars examined, alcohol dehydrogenase (E.C.1.1.1.1) specific activity decreased during the early stages of ripening and then increased in the postclimacteric period. Alcohol dehydrogenase specific activity also increased when immature, mature or pink fruit were placed in an atmosphere of 3% (V/V) oxygen. Measurements of oxygen in the internal tissues and the respiratory quotient throughout ripening established that fruit ripening in air does not suffer an oxygen stress. Increases in alcohol dehydrogenase activity were also observed in pink fruit exposed to 10% (V/V) carbon dioxide. Such atmospheres are known to result in a lowering of the cytoplasmic pH in plants and it is suggested that alcohol dehydrogenase activity is induced during ripening in response to cytoplasmic acid stress. The increased ADH activity during ripening may contribute to flavor development.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe low collagen content in fish muscle makes the quantitative analysis of collagen crosslinks difficult. We have developed a method for the quantitative determination of reducible difunctional collagen crosslinks in samples containing as little as 0.5 picomoles of crosslink per microgram of hydroxyproline. The low collagen‐containing tissue is first enriched by removing most of the non‐collagenous protein with cold sodium hydroxide solution. The lyophilized alkali‐insoluble extract is then reduced with NaB3H4and acid‐hydrolyzed. Initial fractionation of hydrolysates on a Bio‐Gel P‐2 gel filtration column provides partial separation of components with a sharp peak of radioactivity containing more than 90% of the difunctional crosslinks. This peak is ultimately analyzed by HPLC for the quantitative determination of specific difunctional crosslinks. This method has been used to show that the difunctional crosslink composition of muscle collagen from two species of Pacific rockfish differs quantitatively from each other and from that of rat

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTLimited specific hydrolysis of zein by trypsin was used to produce 1.42%, 1.70%, and 1.87% hydrolysates (percentage of peptide bonds cleaved), containing three to four polypeptides (by Fast Protein Liquid Chromatography (FPLC)) ranging in size from ∼16,000 to 3,500 daltons. The mixtures of polypeptides had substantially increased solubilities at pH below 11, including at the isoelectric point of zein (pH 6–7). In general, the emulsifying activity index was less for the hydrolysates than for native zein; the emulsion stability was higher for the 1.70% hydrolysate than was the emulsion of native zein only at pH above 8. At lower pHs, the stability of the emulsions was similar for all samples. The foamability (% overrun) of the hydrolysates was higher than for native zein; the foam stability was higher for the 1.87% hydrolysate than for the other hydrolysates. Phosphorylation and deamidation of the hydrolysates markedly increased the water solubility in the pH range from 4 to 10. Chemical modification of the native zein improved the solubility at pH 2 to 9 after phosphorylation and pH 6 to 11 after deamidation as compared to the native protein. In general, the emulsifying activity index, as well as its stability, was less for the phosphorylated and deamidated hydrolysates than for native zein but the emulsifying activity index of deamidated native zein was higher at pH 7 to 11. Foaming activity and stability of chemically modified hydrolysates were similar to the 1.87% hydrolys

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe enzyme linamarase (E. C. 3.2.1.21) has been purified from cassava cortex (Manihot caculenta) by techniques involving acetone precipitation, ammonium sulfate fractionation, gel filtration and ion‐exchange chromatography.Two peaks of linamarase activity (A&B) were eluted by linear gradient on DEAE‐Sephadex column. Both forms of the enzyme were found to catalyze similar reactions, however, at different rates. Double reciprocal plots from initial velocity data gave Kmof 1.47 mM&1.44 mM for linamarase A&B, respectively, with linamarin as substrate. The Kmvalues with the artificial substrate para‐nitrophenyl glucoside (PNP‐G) were 0.48 mM, Both enzyme forms exhibited maximal activity at pH 6.0 and 30°C.Arrhenius plots gave activation energy (Ea) as 49 KJ/mole (11.72 Kcal mole−1) and 36.5 KJ/mole (8.72 Kcal mole−1) for linamarase A&B, respectively. Analysis of cyanide levels in cassava and its products with the crude enzyme showed the leaves to contain high levels of the

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Book reviewed in this article:Practical Handbook of Biochemistry and Molecular Biology. Edited by Gerald D. Fasman.Chemical Senses. Vol. 2: Irritation. Edited by B. G. Green, J. R. Mason and M. R. Kare.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1990.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY