Starches breakdown

We have already seen several cases in which the synthesis of a class of biomolecules is conducted differently from degradation (glycolysis versus gluconeoge-nesis and glycogen or starch breakdown versus polysaccharide synthesis, for... 

Application of ethylene-,4C to plants resulted in only a 2.4% conversion into soluble carbohydrates, 11% into ether-soluble materials, 6.9% into phytol, 31.7% into cellulose and lignin, and 9.6% into soluble protein and non-protein material, mainly phosphates. 9 Treatment of detached fruit (such as apples, bananas, peaches, figs, and pears) with synthetic auxins, especially (2,4,5-trichlorophenoxy) acetic acid, speeded up ripening, as indicated by color, taste, softness, and starch breakdown. 7 Other fruits have been similarly ripened, 8 and the treatments are effective both on climacteric and non-climacteric fruit. 

Okamoto, K., and Akazawa, T. 1979. Enzymatic mechanism of starch breakdown in germination of rice Oryza sativa cultivar kimmaze seeds. 8. Immunohistochemical localization of j3-amylase. Plant Physiol. 64, 337-340. 

Several enzymes contribute to starch breakdown. Both a- and /J-amylases cleave a(l,4) glycosidic bonds. /J-Amylase catalyzes the successive removal of maltose units from the nonreducing ends of starch chains. Maltose is degraded to form glucose by a-glucosidase. 

Starch breakdown can have dramatic consequences for paper machine operation. The following is a case study reported in the UK [28]. 

Chloroplasts isolated from spinach (Spinacia oleracea) plants grown under controlled light/dark and temperature regimes, contained the phosphorolytic and amylolytic pathways for starch breakdown. The latter consists at least of a- and /3-amylase and /3-D-glucosidase ( maltase ) (see p. 455). 

In a study of the enzyme mechanism of starch breakdown in germinating rice seeds, the localization of the /3-amylase by an immunohistochemical process was described. 

Changes in the isoenzyme pattern of a-amylase have been shown to coincide with the beginning of the starch degradation period in the pods of field beans Vida faba). ° Mesophyll cells of the pods contained the same a-amylase isoenzymes as the endocarp, but exhibited a higher a-amylase activity that parallelled the much higher starch content of this tissue in comparison to the endocarp. Regulation of the starch breakdown was considered to be mediated in part by the formation of a special a-amylase isoenzyme. 

Let us look first at those seeds in which the cotyledons are the storage organs. A number of researchers have used pea seeds (a hypogeal germinator) for their experiments. Unfortunately, variable, sometimes contradictory results have been found, possibly because different varieties have been employed or, more likely, because the experimental conditions were not standardized. Respiration, differentiation of mitochondria, and other sub-cellular changes are all impaired in detached pea cotyledons [10, 112]. The cotyledons therefore seem to require a factor from the axis for the development and maintenance of respiratory metabolism—this can be supplied even by a small piece of attached axial tissue [112, 119]. As far as protein and starch mobilization in peas are concerned it is unclear if the presence of the axis is necessary. In some cases protein and starch breakdown proceed equally well in detached and attached cotyledons [10] but in others both the development of proteinase activity and... 

Diastatic activity Amylolytic or starch-breakdown capacity of malted cereals due to activity of a- and ()-amylases. Diastatic activity is one of the most important parameters associated with malt. 

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