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Starch enzymes affecting

It has been suggested that when plants are subjected to high temperature, starch synthase activity may be rate limiting. At temperatures higher than 30°C, both maize (Singletary et al., 1994) and wheat endosperm (Hawker and Jenner. 1993 Keeling et al, 1993, 1994 Jenner, 1994) had a reduction of starch deposition as compared with lower temperatures. In wheat, the starch biosynthetic enzyme affected was soluble starch synthase (SSS). [Pg.134]

Today, more than 2300 different enzymes are catalogued by the Enzyme Commission of the International Union of Biochemistry (TUB). The enzyme nomenclature proposed by the lUB uses the name of the substrate (the material that is affected by the enzyme) followed by the suffix ase . For example, the enzymes affecting amylum (Latin for starch ) are called amylases. Enzymes affecting lipids, cellulose and proteins are named lipases, cellulases and proteases, respectively. However, many enzymes are still named by their original names. Diastase, trypsin, papain, lactase, etc. are examples of old names which were used before the official TUB names were proposed. Names of proteases originally had the suffix in and are still in use in the traditional industries such as breweries and bread bakeries. [Pg.336]

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. [Pg.138]

More specific hydrolysis may be achieved by the use of enzymes. Thus, the enzyme a-amylase in saliva and in the gut is able to catalyse hydrolysis of al 4 bonds throughout the starch molecule to give mainly maltose, with some glucose and maltotriose, the trisaccharide of glucose. Amylose is hydrolysed completely by this enzyme, but the al 6 bonds of amylopectin are not affected. Another digestive enzyme, a-l,6-glucosidase, is required for this reaction. Finally, pancreatic maltase completes the hydrolysis by hydrolysing maltose and maltotriose. [Pg.485]

The investigations carried out by Professor French and his students were based on sound experimental approaches and on intuitive theoretical considerations. The latter often resulted in new experiments for testing a hypothesis. On the basis of theoretical considerations, Professor French proposed a model for the structure of the amylopectin molecule, and the distribution of the linear chains in this molecule. This model was tested by utilizing enzymes that selectively cleave the linear chains, and the results substantiated the theoretical deductions. He proposed a theory on the nature and types of reactions occurring in the formation of the enzyme - starch complex during the hydrolysis of starch by amylases. In this theory, the idea of multiple attack per single encounter of enzyme with substrate was advanced. The theory has been supported by results from several types of experiments on the hydrolysis of starch with human salivary and porcine pancreatic amylases. The rates of formation of products, and the nature of the products of the action of amylase on starch, were determined at reaction conditions of unfavorable pH, elevated temperatures, and increased viscosity. The nature of the products was found to be dramatically affected by the conditions utilized for the enzymic hydrolysis, and could be accounted for by the theory of the multiple attack per single encounter of substrate and enzyme. [Pg.7]

Enzymes Involved in Starch Biosynthesis. Much of the eady data dealing with starch biosynthesis in plants are derived from the study of various mutants. The shrunken-2 and britde-2 mutants of maize have gready reduced levels of ADPGPP activity owing to the absence of one of the two subunits of this enzyme, and result in a shrunken seed appearance. Mendel s eady work on inheritance of traits was performed with a pea mutant deficient in branching enzyme activity (61). Mutations in plants affecting starch biosynthesis can have severe results to plant morphology and viability. [Pg.254]

A comparison of spontaneously and experimentally released -lactamase preparations of B. licheniformis (40) indicates that the ends of the polypeptide chain can vary without affecting the properties of the enzyme. Although such preparations differ in the C- and N-terminus, they are serologically and catalytically indistinguishable (40,63). Similarly, B. licheniformis 749/C isozymes, separable by starch gel electrophoresis or DEAE-chromatography and believed to differ at the C- or N-terminus (40), have identical substrate specificities (Table V). [Pg.42]


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See also in sourсe #XX -- [ Pg.678 ]




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