Potatoes branching enzymes

Potassium trisiamylborohydride, 20 605 Potassium winchite, 3 289 Potassium-zirconium carbonate, 26 637 Potato branching enzyme, 12 493 Potatoes, citric acid in, 6 632t Potato fungicide, 13 57 Potato starch, 4 724t Potential energy diagrams, 10 118-119 Potential gum test, 12 400 Potentiated toxic effects, 25 214 Potentiometric measurements, 14 612 Potentiometric titrations, 9 585-58 ... 

Potato branching enzyme thus shows a high degree of similarity to maize BEI and to maize BEII isozymes, however to a lesser extent (128, 129). As observed with the maize-branching enzymes, potato BEI was more active on amylose than BEII, and BEII was more active on amylopectin than BEI (130-132). 

Hofvander, P, Andersson, M., Larsson, C. -T., Larsson, H. (2004). Field performance and starch characteristics of high-amylose potatoes obtained by antisense gene targeting of two branching enzymes. Plant Biotechnology Journal, 2, 311-320. 

Phytoglycogen-branching enzyme has been found in du however, no phytoglycogen was isolated by Black et al.23 Preiss and Boyer396 reported that the du mutation lowered starch synthase II activity and also lowered branching enzyme Ha activity. Gao et al.397 used a molecular approach to clone the du gene in maize endosperms and, based on amino acid sequence similarity of the predicted protein product with the soluble starch synthase III of potato,398 concluded that du most likely encodes the 180 000 molecular weight, primer-dependent soluble starch synthase described previously.399,400,401... 

As indicated in Table 4.12, four regions which constitute the catalytic regions of amylolytic enzymes are conserved in the starch-branching isoenzymes of maize endosperm, rice seed and potato tuber, and the glycogen-branching enzymes of E. coli.286,281 It would be of interest to know whether the seven highly conserved amino acid residues of the a-amylase family listed in bold letters in Table 4.12 are also functional in branching enzyme catalysis. Further experiments, such as chemical modification and analysis of the three-dimensional structure of the BEs, would be needed to determine the nature of its catalytic residues and mechanism. 

Earlier studies on the properties of phosphorylases isolated from various sources have indicated that their subunits are similar in size with about 100,000 daltons.15-17 The reaction proceeds in a rapid equilibrium random Bi-Bi mechanism as has been shown by kinetic studies with rabbit skeletal muscle phosphorylases a18-20 and b,21,22 rabbit liver enzyme,23 potato tuber enzyme,24 and the enzyme from E. coli.25) In contrast, the substrate specificities for various glucans differ considerably depending on the enzyme sources. The rabbit muscle enzyme has high affinity for branched glucans such as glycogen and amylopectin but low affinity for amylose and maltodextrin.26,27 The potato tuber enzyme can act on amylose, amylopectin, and maltodextrin but only poorly on glycogen,28,29 while the E. coli enzyme shows high affinity for maltodextrin.10 ... 

Borovsky, D., Smith, E. E., and Whelan, W. J. 1975. Purification and properties of potato 1,4-a-D-glucan 1,4-a-D-glucan, 6-a-(l,4-a-D-glucano)-transferase. Evidence a dual catalytic function in amylose branching enzyme. Eur. J. Biochem. 59, 615-625. 

Khoshnoodi, J., Ek, B., Rask, L., and Larsson, H. 1993. Characterization of the 97 and 103-KDa forms of starch branching enzymes from potato tubers. FEBS Lett. 332,132-138. 

Kossmann, J., Visser. R. F., Miiller-R6ber, B. T., Willmitzer, L., and Sonnewald. U. 1991. Cloning and expression analysis of a potato cDNA that encodes branching enzyme Evidence for coexpression of starch biosynthetic genes. Mol. Gen. Genet. 230, 39-44. 

Kram, A., Oostergetel, G. T., and van Bruggen. E. F. J. 1993. Localization of branching enzyme in potato tuber cells with the use of immunoelectron microscopy. Plant Physiol. 101, 237-243. 

Vos-Scheperkeuter, G. H., de Wit, J. G., Ponstein, A. S., Feenstra, W. J., and Witholt, B. 1989. Immunological comparison of the starch branching enzymes from potato tubers and maize kernels. Plant Physiol 90,75-84. 

Larsson CT, Hofvander P, Khoshnoodi J, Ek B, Rask L, Larsson H. Three isoforms of starch synthase and two isoforms of branching enzyme are present in potato tuber starch Plant Sci. 2001 117 9-16. 

Jobling SA, Schwall GP, Westcott RJ, Sidebottom CM, Debet M, Gidley MJ, Jeffcoat R, Safford R. A minor form of starch branching enzyme in potato (Solanum tuberosum L.) tubers has a major effect on starch structure cloning and characterisation of multiple forms of SBEA. Plant J. 1999 18 163-171. 

Rydberg, U, Andersson, L, Andersson, R, Aman, P and Larsson, H. Comparison of starch branching enzyme I and B from potato 2001 Eur. J. Biochem. 268 6140-6145. 

To produce amylopectin, it is necessary to have a starch branching enzyme that is capable of introducing the a-(1 6) branch linkages into the linear amylose molecules synthesized by starch synthase. Such an enzyme (Q-enz)mre) was first identified in potatoes [131] and then in broad beans [132]. The potato Q-enzyme has been isolated and purified and the properties determined [133]. Q-enzyme is a glucanyltransferase and cleaves an a-jl— 4) linkage of an amylose chain, and then transfers the chain to the C6-OH of another amylose-chain, rather than being transferred and attached to the residual part of the cleaved chain [134]. It was shown that water is not involved in these branching reactions [133]. 

The specificity of potato Q-enzyme h been examined in some detail. With amylose as donor substrate, the DP must exceed 40 n-glucose residues for rapid transglucosylation to occur with a branched polysaccharide as donor, the outer chains must exceed 14 n-glucose residues. Since linear chains of this length are not attacked by Q-enzyme, there are evidently multiple sites for the binding of Q-enz3une and its substrate. 

Both described enzymes are isolated from natural sources. Phosphorylase is isolated from potatoes whereas the glycogen branching enzyme is produced by various bacterial sources. Depending on the source the properties of the products and the reaction conditions may differ. 

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