Enzyme temperature

Enzyme Temperature (°C) Pressure (MPa) Time (h) Effect Reference... 

Reagents for enzyme measurement are known not to be optimal for the different species (e.g., the substrate concentrations required for the measurement of plasma aspartate aminotransferase [AST/GOT] in rats, dogs, and monkeys differed from the concentrations used for these human plasma enzymes (Dooley 1979). However, there remains a lack of data on the optimal conditions—in terms of buffer, substrate concentration, reaction times, etc.— required for the different species. There are no nationally or internationally agreed-upon recommendations for laboratory animal samples, so most analysts use reagents formulated for human enzymes. Temperature... 

Further, the change in the tumor microenvironment such as pH, enzyme, temperature, and redox potential can be used to further control the drug release at the target site... 

Endo-acting a-amylases that produce large quantities of maltohexaose from starch are secreted by various bacilli. Bacillus circulans strains G-6 (41) and F-2 (42) were discovered independently and shown to produce such enzymes. Temperature and pH optima vary considerably between these enzymes, strain F-2 producing the more temperature stable (opt. SO C) amylase with a lower pH optimum for activity (6-6.5). This enzyme also has considerable activity on raw starch (43). 

The concept of equilibrium is also important in biochemical processes such as O2/CO2 exchange in hemoglobin (for example, see exercise 5.8 at the end of this chapter), the binding of small molecules to DNA strands (as might occur in the transcription process), and the interaction of substrates and enzymes. Temperature effects are important in protein denaturation process. Clearly, the ideas established in this chapter are widely applicable to all chemical reactions, even very complex ones. 

Most enzymes work best within a narrow pH range and are susceptible to a wide variety of compounds which inhibit or sometimes promote the activity. The majority of enzymes work most efficiently at around 40°C and at higher temperatures are rapidly destroyed. 

The effect of temperature is complex, but the majority of enzymes are most active about 45 and all are completely destroyed at 100 . At o the activity is reduced considerably but the enzyme is not destroyed. 

It should be noted that a number of different enzyme preparations can now be purchased directly from manufacturing chemists. It must be emphasised that the activity of an enzyme, whether purchased or prepared in the laboratory, may vary between rather wide limits. The activity is dependent on the source of the enzyme, the presence of poisons and also on the temperature. It appears, for example, that the quality of horseradish peroxidase depends upon the season of the year at which the root is obtained from the ground. It cannot be expected therefore that all the experiments described below will work always with the precision characteristic of an organic reaction proceeding under accurately known conditions. 

To this yellow solution add the enzyme solution, mix well and allow to stand at room temperature. The mixture becomes red as the pH rises to 8. 

Fill two burettes A and B w ith A//10 HCl. Run in from A, drop by drop, sufficient A/,To hydrochloric acid just to discharge the red colour in A. Maintain the temperature at about 60° and keep the colour just discharged by cautiously adding the HCl from time to time. Care must be taken not to add an excess of acid, otherwise the proteins will be precipitated and the enzyme rendered inactive. The reaction is o>m plete in about 5 minutes, but allow the mixture to stand for a further 5 minutes after the final discharge of the colour. 

Recently, the use of Hpase enzymes to iateresterify oils has been described (23). In principle, if a 1,3-speciftc Hpase is used, the fatty acid ia the 2 position should remain unchanged and the randomization occur at the terminal positions. However, higher temperatures, needed to melt soHd fats, may cause a 1,2-acyl shift and fatty acids are scrambled over all positions. 

The extension of the useful storage life of plant and animal products beyond a few days at room temperature presents a series of complex biochemical, physical, microbial, and economic challenges. Respiratory enzyme systems and other enzymes ia these foods continue to function. Their reaction products can cause off-davors, darkening, and softening. Microbes contaminating the surface of plants or animals can grow ia cell exudates produced by bmises, peeling, or size reduction. Fresh plant and animal tissue can be contaminated by odors, dust, iasects, rodents, and microbes. 

Plasteins ate formed from soy protein hydrolysates with a variety of microbial proteases (149). Preferred conditions for hydrolysis and synthesis ate obtained with an enzyme-to-substrate ratio of 1 100, and a temperature of 37°C for 24—72 h. A substrate concentration of 30 wt %, 80% hydrolyzed, gives an 80% net yield of plastein from the synthesis reaction. However, these results ate based on a 1% protein solution used in the hydrolysis step this would be too low for an economical process (see Microbial transformations). 

Pectic enzymes are inactivated by pasteurization. Citms juices require higher temperatures for enzyme deactivation than for pasteurization. Heat treatment at 85—94°C for 30 s inactivates pectic enzymes (9) and is more than adequate for pasteurization. 

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