Khandke K M, Vithayathil P J, Murthy S K
Department of Biochemistry, Indian Institute of Science, Bangalore.
Arch Biochem Biophys. 1989 Nov 1;274(2):501-10. doi: 10.1016/0003-9861(89)90463-3.
Proteins from the culture filtrates of Thermoascus aurantiacus grown on paper were found to hydrolyze larchwood xylan completely to form xylose and 4-O-methyl-alpha-D-glucuronic acid. Partial hydrolysis of xylan by a xylanase purified from the culture filtrates resulted in the formation of neutral xylooligosaccharides of dp from 2 to 6 and acidic xylooligosaccharides of dp from 5 to 8. Each of these acidic sugars contained a single molecule of 4-O-methyl-alpha-D-glucuronic acid as a branch. Extensive hydrolysis of these oligosaccharides or xylan by xylanase led to the isolation of xylose, xylobiose, and an aldotetrauronic acid as terminal products. The structure of the aldotetrauronic acid was established by NMR as (2(2)-O-alpha-D,4-O-methyl-alpha-D-glucurono)-xylotriose. A beta-glucosidase, also purified from the culture filtrates, hydrolyzed xylan and the neutral or the acidic xylooligosaccharides from the nonreducing end to release only xylose. Neither xylanase nor beta-glucosidase hydrolyzed the beta-(1----4) linkage between the xylose carrying the branch and the adjacent xylose residue on each side.
研究发现，在纸张上生长的嗜热栖热放线菌培养滤液中的蛋白质可将落叶松木聚糖完全水解，生成木糖和4-O-甲基-α-D-葡萄糖醛酸。从培养滤液中纯化得到的木聚糖酶对木聚糖进行部分水解，生成了聚合度为2至6的中性木寡糖和聚合度为5至8的酸性木寡糖。这些酸性糖中的每一种都含有一个单分子的4-O-甲基-α-D-葡萄糖醛酸作为分支。木聚糖酶对这些寡糖或木聚糖进行广泛水解后，分离得到了木糖、木二糖和一种醛糖四糖酸作为终产物。通过核磁共振确定醛糖四糖酸的结构为(2(2)-O-α-D,4-O-甲基-α-D-葡萄糖醛酸基)-木三糖。同样从培养滤液中纯化得到的β-葡萄糖苷酶从非还原端水解木聚糖以及中性或酸性木寡糖，只释放出木糖。木聚糖酶和β-葡萄糖苷酶均不水解带有分支的木糖与两侧相邻木糖残基之间的β-(1→4)键。
