Urea, enzyme activity

Anemia, increased liver enzyme activity, increased cholesterol and urea Decreased body growth decreased testes weight... 

Cows and calves fed low-zinc diets of 25 mg Zn/kg ration showed a decrease in plasma zinc from 1.02 mg/L at start to 0.66 mg/L at day 90 cows fed 65 mg Zn/kg diet had a significantly elevated (1.5 mg Zn/L) plasma zinc level and increased blood urea and plasma proteins (Ram-achandra and Prasad 1989). Biomarkers used to identify zinc deficiency in bovines include zinc concentrations in plasma, unsaturated zinc-binding capacity, ratio of copper to zinc in plasma, and zinc concentrations in other blood factors indirect biomarkers include enzyme activities, red cell uptake, and metallothionein content in plasma and liver (Binnerts 1989). 

These changes in demand for urea cycle activity are met over the long term by regulation of the rates of synthesis of the four urea cycle enzymes and carbamoyl phosphate synthetase I in the liver. All five enzymes are synthesized at higher rates in starving animals and in animals on veiy-high-protein diets than in well-fed animals eating primarily carbohydrates and fats. Animals on protein-free diets produce lower levels of urea cycle enzymes. 

Amylase activity decreased within the series of chlorosubstituted ureas, decreased activity varied directly with water solubility, suggesting an adsorptive effect on the enzyme surface. The enzyme effects were not considered to be major causes of growth inhibition.172... 

Urease activity persists unaltered when the enzyme is dissolved in SM urea although the ultracentrifuge data indicate a molecular weight of about 90,000 (7). This form of urease has not been sufficiently characterized but does indicate that neither enzymic activity nor specific activity is dependent upon very high molecular weight aggregates. 

Solution in 0.1 M acetate buffer, pH 3.5, resulted in an enzymically active species (8n) of 240,000 daltons (46). Tanis and Naylor (47) have reported that at low concentration of protein the 18 S form predominated above pH 5.3 and the 12 S form below pH 4.8. Between these pH values a rapid equilibrium of the 12 S and 18 S species was observed The dissociation behavior of urease at low pH depends on the buffer used. In 0.1 M potassium phosphate buffer, adjusted to pH 2.0 with HC1, a heterogeneous mixture of dissociated forms was obtained (d) with an Mw of about 150,000. In acetate buffer at pH 3.5 dissociation into a 120,000 molecular weight species (4n) was observed (48). In 34% acetic acid at pH 2.2 there is effected a dissociation to subunits (n) of 30,000 daltons (7). This same value was obtained for urease ultracentrifuged in 8 M urea -f- 0.5 M thiol and in performic acid oxidized urease (48). 

Second, the correlation of change in enzymic activity with the titration of essential sulfhydryl groups has led to a postulation of eight active sites per 480,000 (56). Unfortunately, the possibility of structural changes during such titrations makes interpretation of such data equivocal. However, the observation that urease retained its activity in 8 M urea, where the molecular weight has been reduced at least to 90,000 (7), supports the conclusion above. 

Cyanuric fluoride has been used to modify tyrosine residues, substituting the phenolic hydroxyl group. A maximum of 3 residues in RNase was found to react at pH 10.9 and 25° (148a). However, some mystery surrounds this number, as with other estimates of accessibility, since alkaline-denatured material where all tyrosine residues are available still showed the reaction of only 3 residues with cyanuric fluoride. However, similar observations have been made on iodination in 8 Af urea (11 )- At pH 9.3, Takenaka et al. (149) found that only 2 residues reacted and that 115 was not one of them. Two more reacted after alkali denaturation. Two were resistant under all conditions tested. No enzymic activity data were reported. 

Nelson and Hummel 351) made a careful investigation of the urea transition near pH 7. Their absorbance difference spectra clearly show changes in the environment of phenylalanine as well as tyrosine residues. The optical rotation changes occur in the same range of urea concentrations. The loss of enzymic activity (U>p) is biphasic. At low urea con-... 

Nieuwlandt, D., West, M., Cheng, X., Kirshenheuter, G, Eaton, B.E. The first example of an RNA urea synthase selection through tire enzyme active site of human neutophile elastase. ChemBioChem4, 649-662(2003). 

Metabolites and substrates (urea, triglycerides, bili-rubine, lactate), enzymes (the measurands are the enzyme activities), hormones (aldosterone, estradiol, es-triol, testosterone, thyroxin), drugs (theophylline, digoxin, digitoxin), total proteinAs far as possible, isotope dilution mass spectrometry is used for the primary measurements in both institutes (e.g. [4]). 

The keratin structure is destroyed through the use of proteolytic enzymes such as pronase and proteinase K. They are often used with chemical agents such as urea and thioglycolic to cleave the disulfide bonds and increase the dissolution rate of enzyme activity. The extracting procedures, using enzymatic digestion, last about 4-6 h and must be conducted at constant temperature and pH for providing maximum enzyme activity [155],... 

As described earlier, although water (i.e., moisturization) is required to alleviate dry skin, reduced enzymic activity is the cause of the scaling symptoms associated with the condition. These enzymes can be activated for instance with glycerol,31 hydroxyacids,25 or urea,32 but to retain full desquama-tory activity topical application of enzymes is required. As all corneodesmosomal proteins persist in the superficial layers of the SC in dry skin, either the full spectrum of skin desquamatory enzymes are required to maximally induce exfoliation or broad specificities are needed in a single enzyme. 

Corn starch for use in an enzymic conversion process should not contain more than 0.4% protein. In some cases modified starches, such as starch ethers, are used as feedstock. Higher product cost is balanced by the substantial reduction of retrograda-tion in products thus obtained. The feedstock has to be buffered in order to reach the required pH level for optimum enzyme activity in the process water of the paper mill. Additional adjustments may be required at the mill site when filtered surface water, which varies with the seasons, is used. Calcium salts for improved heat stability of the enzyme are added by the starch supplier or the paper mill. Further addition of sodium chloride will promote enzyme activity, and urea will broaden the critical pH range. Starch preservatives have to be added after the enzyme has been inactivated. 

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