Takaha T, Yanase M, Okada S, Smith S M
Institute of Cell and Molecular Biology, University of Edinburgh, United Kingdom.
J Biol Chem. 1993 Jan 15;268(2):1391-6.
Disproportionating enzyme (D-enzyme, 4-alpha-glucanotransferase; EC 2.4.1.25) has been purified to homogeneity from potato tubers and its activity characterized. The enzyme catalyzes the transfer of maltooligosaccharides from one 1,4-alpha-D-glucan molecule to another, or to glucose. Maltooligosaccharides are effective donor molecules, but short chain amylose and amylopectin may also function as donors. Enzyme activity is not affected by inorganic phosphate, 3-phosphoglycerate, or hexose phosphates. A cDNA clone encoding the enzyme was isolated using oligonucleotide probes derived from partial peptide sequences of the purified enzyme. The identity of the cDNA clone was confirmed by expression in Escherichia coli resulting in D-enzyme activity. The amino acid sequence deduced from the cDNA shows significant homology with a 4-alpha-glucanotransferase from Streptococcus. The deduced sequence indicates the presence of an amino-terminal plastid transit peptide of 52 amino acid residues and a mature polypeptide of 524 residues. D-enzyme mRNA is present in leaves, stems, roots, and stolons but is most abundant in developing and mature tubers. The amount of mRNA in leaves increases in response to light and to sucrose added to the medium. These results are discussed in terms of the function of D-enzyme in potato starch metabolism.
歧化酶（D - 酶，4-α-葡聚糖转移酶；EC 2.4.1.25）已从马铃薯块茎中纯化至同质，并对其活性进行了表征。该酶催化麦芽寡糖从一个1,4-α-D-葡聚糖分子转移至另一个分子，或转移至葡萄糖。麦芽寡糖是有效的供体分子，但短链直链淀粉和支链淀粉也可作为供体。酶活性不受无机磷酸盐、3-磷酸甘油酸或己糖磷酸的影响。利用从纯化酶的部分肽序列衍生而来的寡核苷酸探针，分离出了编码该酶的cDNA克隆。通过在大肠杆菌中表达产生D - 酶活性，证实了该cDNA克隆的身份。从cDNA推导的氨基酸序列与来自链球菌的4-α-葡聚糖转移酶具有显著同源性。推导序列表明存在一个由52个氨基酸残基组成的氨基末端质体转运肽和一个由524个残基组成的成熟多肽。D - 酶mRNA存在于叶片、茎、根和匍匐茎中，但在发育中的和成熟的块茎中含量最高。叶片中mRNA的量会因光照和添加到培养基中的蔗糖而增加。本文根据D - 酶在马铃薯淀粉代谢中的功能对这些结果进行了讨论。
