Enzyme activity, heat

Moisture is one of the most important parameters because it affects yields and stability during storage. Cereals not stored at their optimum moisture (>14%) have more enzyme activity, heat damage, and insect/mold damage, and might require drying. 

Similar to nNOS, Ca2+-activated calmodulin is important for the regulation of eNOS activity. However, several other proteins interact with eNOS and regulate its activity. Heat shock protein 90 (hsp90) is found associated with eNOS and probably acts as an allosteric modulator that activates the enzyme. Caveolin-1 binds eNOS and directs it to caveolae. Caveolin-1 is viewed as an inhibitor of eNOS activity, which is being replaced by CaM upon activation of endothelial cells [2]. 

From the results of the urease activity test summarized in Figure 15, it is clear that the deposition procedure preserved to a certain extent the enzyme catalytic activity. Heating the sample before testing decreased the enzyme in the film by about 30% but did not eliminate it completely. The results of the activity test of two samples are summarized in Table 1 together with reference values for a spontaneous reaction without enzyme. It is necessary to underline that enzymatic activity on spherical supports was higher than the respective value in flat films, which could indicate that apparent catalytic efficiency was improved due to an increased area-to-volume ratio. 

Both the active enzyme, the heat-inactivated enzyme from Sulfurospirillum (Dehalos-pirillum) multivorans, and cyanocobalamin are capable of dehalogenating haloacetates (Nenmann et al. 2002), and the rate of abiotic dehalogenation depends on the catalyst that is nsed. 

Enzyme activity can indicate the exposure of honey to heating and long storage. This criterion is not more accurate than the HMF content value because enzyme activities vary with honey samples. The diastase activity is usually associated with heat treatment. However, its activity gives only an indication about the processing (heat treatment) of the honey but is not suitable for the detection of the origin. 

By a careful fractionation of normal horse serum, involving as an essential part of the process a separation of closely related substances by the Schtitz168 foam technique, Bader, Schiitz and Stacey16 obtained a crystalline mucoprotein with high choline esterase activity. This appears to be the first mucoprotein obtained without the use of heat or alcohol, and while it is not yet claimed that the crystalline material is indeed the enzyme itself, arguments are advanced to show that the enzymic activity is closely bound up with mucoprotein structure. 

In addition there is other evidence pointing to the fact that the same enzyme is involved in reactions with both D-fructose and L-arabinose. First, the relative rates of reaction with D-fructose and L-arabinose, respectively, remain constant after partial inactivation of the enzyme by heat. Second, the enzyme catalyzing both reactions is produced to a marked extent when sucrose is used as substrate for the growth of the organisms, but not when D-glucose or L-arabinose is used sucrose phos-phorylase is an adaptive enzyme. Third, on fractionation of the enzyme preparation with various concentrations of ammonium sulfate, the relative activities of the fractions are the same for both sugars. These observations indicate not only that the same enzyme is involved in both reactions but also that no additional enzyme is required for the formation of D-glucosyl-L-arabinose. 

One of the issues of the industrial process design is related to the heat released by this reaction. A temperature rise will decrease the acetic acid yield, not only because the equilibrium constant becomes lower (the reaction is exothermic see section 2.9) but also because it will reduce the enzyme activity. It is therefore important to keep the reaction temperature within a certain range, for instance, by using a heat exchanger. However, to design this device we need to know the reaction enthalpy under the experimental conditions, and this quantity cannot be easily found in the chemical literature. 

As we saw earlier in this chapter, substrates are the molecules which undergo chemical change as a result of enzyme activity. Many enzymes will only operate when in the presence of essential co-factors or coenzymes. The term coenzyme is not entirely appropriate as it implies that, like enzymes themselves, these compounds do not undergo chemical change. This is not true and more accurate terminology would be co-substrate. Coenzymes are always much smaller than the enzymes with which they operate and are not heat sensitive as are the proteins. 

Serum alkaline phosphatase elevations have been reported following administration of salt-poor albumin (B5). Placenta is very rich in a heat-stable alkaline phosphatase, and albumin prepared from placental blood has a high activity of this enzyme. In one cirrhotic patient who received 1-6 units per day of albumin obtained from pooled human blood and/or human placenta, the alkaline phosphatase before infusion was 5 Bodansky units and by the thirteenth day of administration had reached a value of 160 units. The physician administering the albumin at first thought the patient was having a severe toxic liver reaction and stopped the therapy. The alkaline phosphatase then started to go down and within 10 days returned to normal levels. Analysis of the albumin indicated that it contained 470 units of alkaline phosphatase activity and was probably responsible for the observed elevations in the serum enzyme activity. Albumin prepared from venous blood did not cause an alkaline phosphatase elevation, but placenta-albumin caused elevations with a half-life of about 8 days (Ml). 

The elimination or inactivation of enzymes used to treat proteins is a critical problem once the desired modification in functionality is achieved. In many instances, product inhibition or self destruction does not occur as noted above for fish protein concentrate. As stated by Puski (20), if heat inactivation is used, the proteins may be denatureT"and revert to insoluble forms. Washing out the enzyme at its isoelectric point would also remove a portion of the protein which is solubilized by the enzyme. Inactivation of enzymes by chemical means may also cause significant changes in the protein. Thus, while desired functional modifications of food ingredients may be obtained through enzyme treatment, the problem of latent enzyme activity in food formulations must be addressed. 

L-lysine, L-threonine or L-methionine protect the enzymic activity against heat inactivation [8]... 

At higher temperatures, the enzyme activity decreases more rapidly with incubation time. The heat inactivation of many enzymes follows such patterns. 

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