Enzymes calcium-containing

Thermolysin (EC 3.4.24.4) a heat-stable, zinc- and calcium-containing neutral protease, M, 37,500, from Bacillus thermoproteolyticus, with a substrate specificity similar to that of Subtilisin (see). After one hour at 80 °C, T. still has 50% original activity. This high heat stability of T. is attributed to the large number of hydrophobic regions and the presence of four bound calcium ions, which serve in place of disulfide bridges (T. contains no disulfide bridges) to maintain the compact shape of the molecule. T. is neither a thiol nor a serine enzyme. 

Many enzymes incorporate one or more metal ions as essential parts of their structure. Different metalloenzymes make use of ions of magnesium, calcium, manganese, iron, cobalt, copper, zinc, or molybdenum. For example, the molecule of alcohol dehydrogenase (molecular mass 87000 d), which catalyzes the oxidation of ethanol to acetic acid in the human liver, contains two atoms of zinc, and the amylase in human saliva contains an atom of calcium (Ca" " ). Some enzyme molecules contain several metal atoms, which may be of different kinds. An example is cysteamine oxidase, which catalyzes the oxidation of cysteamine, HSCH2CH2NH2 this enzyme contains an atom of iron, an atom of copper, and an atom of zinc. 

Paraoxonase/arylesterase from human serum and other manunalian species catalyzes the hydrolysis of organophosphates, aromatic carboxylic acids and possibly carbamates (Primo-Parmo et al. 1996). Paraoxonase (PONl) is so called because paraoxon is the substrate commonly used to measure its enzyme activity (Mackness et al. 1998). The crystal structure of PONl family of calcium-containing... 

ThermalLkjucfaction Process. In the thermal Hquefaction process (see Eig. 1), a starch slurry containing no enzyme or added calcium is heated for several minutes. The slurry is slightly acidic and sufficient acid Hquefaction is achieved to reduce viscosity. The hydrolyzate (at essentially zero DE) is flash-cooled to 95—100°C, a-amylase is added, and the pH is adjusted. The reaction then goes to completion. 

Milk from cows contains 3.2% protein, about 80% of which is casein. Casein is isolated by a precipitation process from milk, involving heating, rinsing to remove whey, and drying to a powder. The yield is about 3 kg/ 100 kg skim milk. Rennet casein is obtained when the casein is precipitated by chymosin enzyme, also known as rennet, and acid casein is produced when precipitation is accomplished by acidification. Acid casein is usually found in the form of sodium caseinate or calcium caseinate, which are water-soluble salts. Caseinates are made by reacting NaOH or CaOH with a slurry of casein curd or powder and then spray drying (Southward, 2010). 

As mentioned above, certain metal ions may be necessary for activity or stability. Thus calcium is needed for bacterial a-amylase. Magnesium or cobalt is needed with glucose isomerase. Calcium stabilises the starch-liquifying bacterial a-amylases but inactivates the glucose isomerase that may be used subsequently. Many enzymes contain an additional non-... 

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