Potato D-enzyme

Takaha, T., Yanase, M., Takata, H., Okada, S., and Smith, S. M. 1996. Potato D-enzyme catalyzes the cyclization of amylase to produce cycloamylose, a novel cyclic glucan. J. Biol. Chem.,271, 2902-2908. 

R-Enzyme was first isolated from broad beans and potatoes by Peat and coworkers. Purification was difficult in view of the relatively small amounts present and the large number of contaminating enzymes, particularly a maltodextrinyl transferase (D-enzyme), branching (Q-) enzyme, and alpha-amylase. However, a procedure was developed that gave preparations suflBciently pure to permit routine use of this enzyme during some ten years for debranching of amylaceous polysaccharides. ... 

Disproportionating (D) Enzyme. An enzyme from potato tubers catalyzes a reversible transfer of glucose-a-1-4 linkages, but it transfers 2 sugar residues, a maltose unit. The donor of such a unit may be as small as maltotriose (3 glucose residues) and may be a large starch molecule. The transfer builds up linear polymers of glucose (amylose). 

These phenomena appear to indicate that the less purified potato phosphorylase (I) is contaminated by a disproportionating enzyme, most probably D-enzyme, or a special kind of a-amylase (16,23). The use of purified enzyme did not confirm this assumption. On the contrary, the effect was rather pronounced. 

Reaction of amylose (d.p. 2000) with potato disproportionating enzyme (D-... 

Amylo-1 —> 6-glucosidase obtained by Cori and Larner218 from rabbit muscles, and R-enzyme isolated by Hobson, Whelan and Peat219 from potatoes and broad beans, are typical debranching enzymes, which will hydrolyze the 6 — 1-a-D-glucosidic linkage rather than the normal 4 —> 1-a-D linkage. These enzymes will therefore be particularly important in determinations of the fine structure of amylopectin, if they can be sufficiently well purified. 

Jarvis, M. C., Threlfall, D. R., Friend, J. (1981b). Potato cell wall polysaccharides degradation with enzymes from Phytophthora infestans. J. Exp. Bol, 32,1309-1319. 

Richardson, S., Nilsson, G., Cohen, A., Momcilovic, D., Brinkmalm, G., Lo Gorton, G. (2003). Enzyme-aided investigation of the substituent distribution in cationic potato amylopectin starch. Anal. Chem., 75, 6499-6508. 

McCue, K. F., Shepherd, L. V. T., Allen, P. V, Maccree, M. M., Rockhold, D. R., Corsini, D. L., Davies, H. V, Belknap, W. R. (2005). Metabolic compensation of steroidal glycoalkaloid biosynthesis in transgenic potato tubers using reverse genetics to confirm the in vivo enzyme function of a steroidal alkaloid galactosyltransferase. Plant science, 168, 267-273. 

In a similar use of a-amylase, Parrish and Whelan249 treated potato starch with crystalline human salivary a-amylase and obtained a phosphorylated maltotetraose that had previously been reported by Postemak250 and that was the smallest phospho-dextrin formed. They determined its structure to be 63-phosphomaItotetraose, similar in structure to the smallest a-limit dextrin, 63-a- D-glucopyranosylmaltotriose, formed by this enzyme and porcine pancreatic a-amylase. 

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