Browning, enzymic

W.H. Scouten, J.H. Luong, and R.S. Brown, Enzyme or protein immobilization techniques for applications in biosensor design. Trends Biotechnol. 13,178—185 (1995). 

Mechanisms of catalase and peroxidase catalysis. Attention has been focused on a series of strikingly colored intermediates formed in the presence of substrates. When a slight excess of H202 is added to a solution of horseradish peroxidase, the dark brown enzyme first turns olive green as compound I is formed, and then pale red as it turns into compound II. The latter reacts slowly with substrate AH2 or with another H202 molecule to regenerate the original enzyme. This sequence of reactions is indicated by the colored arrows in Fig. 16-14, steps a-d. 

Manufacturers of black tea do not steam the leaves they crush and ferment them. This releases the browning enzymes, allowing them to go to work. Antioxidant effects are not destroyed, because the products of the fermentation also have free-radical-neutralizing effects. 

G. M. Brown, Enzymic synthesis of pterins and dihydropteroic acid, Chem. Biol. Pteridines, Proc. 4th Int. Symp., 1970, pp. 243-264. 

The browning of plant tissues which occurs during the formation of the coats of the seeds, fruits and vegetables, in barks, and in the spores of fungi is associated with the oxidation mainly, of various phenolic substances. However, daphnetin, esculetin and some other coumarin derivatives have also been included in the numerous substrates for the browning enzymes responsible for these processes [166—173]. The enzymes catalysing these changes are oxidases and phenolases, and perhaps they also participate in the synthesis and biotransformation of the various coumarins [174—177]. 

Frozen Food. The chelating and acidic properties of citric acid enable it to optimize the stabiUty of frozen food products by enhancing the action of antioxidants and inactivating naturally present enzymes which could cause undesirable browning and loss of firmness (57,58). 

Figure 4.19 Schematic and topological diagrams for the structure of the enzyme carboxypeptidase. The central region of the mixed p sheet contains four adjacent parallel p strands (numbers 8, 5, 3, and 4), where the strand order is reversed between strands 5 and 3. The active-site zinc atom (yellow circle) is bound to side chains in the loop regions outside the carboxy ends of these two p strands. The first part of the polypeptide chain is red, followed by green, blue, and brown. (Adapted from J. Richardson.)...

Figure 4. The citrate cycle. There is complete oxidation of one molecule of acetyl-CoA for each turn of the cycle CH3COSC0A + 2O2 - 2CO2 + H2O + CoASH. The rate of the citrate cycle is determined by many factors including the ADP/ATP ratio, NAD7NADH ratio, and substrate concentrations. During muscle contraction, Ca is released from cellular stores (mainly the sarcoplasmic reticulum) and then taken up in part by the mitochondria (see Table 2). Ca " activates 2-oxoglutarate and isocitrate dehydrogenases (Brown, 1992). Succinate dehydrogenase may be effectively irreversible. Enzymes ...

Roy, A. V. Brown, M. E. and Hayden, J. E. Sodium thymolphthalein monophosphate, a new acid phosphatase substrate with greater specificity for the prostatic enzyme in serum. Clin. Chem. (1971), IJ, 1093-1102. 

Culley FJ, Brown A, Conroy DM et al (2000) Eotaxin is specifically cleaved by hookworm metal-loproteases preventing its action in vitro and in vivo. J Immunol 165 6447-6453 Davis DA, Singer KE, De La Luz Sierra M et al (2005) Identification of carboxypeptidase N as an enzyme responsible for C-terminal cleavage of stromal cell-derived factor-lalpha in the circulation. Blood 105 4561 568... 

Caramel color interacts with other food components. As an example, a concentration higher than 700 ppm caramel in cola increased the rate of hydrolysis of the aspartame, forming alpha-L-aspartyl-L-phenylalanine. Caramelization products inhibited enzymic browning by 85.8 and 72.2% when heated at pH 4 and 6, respectively, for 90 min. The highest inhibitory activity was found for the fraction with molecular weight of 1000 to 3000. Caramel is often used for adulteration of juices and other foods like honey or coffee. It can be determined by quantification of marker molecules such as 5-HMF, 4-Mel, and DFAs. ... 

The conjugation of catechin on poly(allylamine) using ML as catalyst was examined under air. During the conjugation, the reaction mixture turned brown and a new peak at 430 nm was observed in the UV-vis spectrum. At pH 7, the reaction rate was the highest. The conjugation hardly occurred in the absence of laccase, indicating that the reaction proceeded via enzyme catalysis. 

Watermelon cell walls, prepared as follows, were kindly provided by Dr. Niels O. Maness of the Department of Horticulture and Landscape Architecture of Oklahoma State University. Ripe watermelon mesocarp tissues were placed on ice, diced into small pieces, and then homogenized on ice in Tris-saturated phenol to give enzymically inactive watermelon cell walls [6]. The solids were collected on two layers of mira cloth and washed with water until the smell of phenol was gone. The crude cell walls were further washed with chloroform methanol (1 1, W/V) and acetone until a fluffy consistency was obtained. The acetone-washed cell wall residue was dried in an oven at 60 °C and stored in a brown bottle. 

Berg R. H., G. W. Erdos, M. Gritzali and R. D. Brown. (1988). Enzyme-gold affinity labeling of cellulose. Journal of Electron Microscopy Techniques 8 371-379. 

Fall RR, JI Brown, TL Schaeffer (1979) Enzyme recruitment allows the biodegradation of recalcitrant branched hydrocarbons by Pseudomonas citronellolis. Appl Environ Microbiol 38 715-722. 

Pierattelli R, L Banci, NA Eady, J Bodiguel, JN Jones, PCE Moody, EL Raven, B Jamart-Gregoire, K A Brown (2004) Enzyme-catalyzed mechanism of isoniazide activation in Class I and Class III peroxidases. J Biol Chem 279 39000-39009. 

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