The subunit structure of beta-glucosidase from Botryodiplodia theobromae Pat.
The subunit structure of beta-glucosidase from Botryodiplodia theobromae Pat.
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DOI：
10.1042/bj1450361
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发表时间：
1975-02
期刊：
影响因子：
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通讯作者：
G. M. Umezurike
中科院分区：
文献类型：
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作者：
G. M. Umezurike
1.在以棉花绒（纤维素）为碳源生长4-8周的Botryodiplodia theobromae Pat培养物中观察到一系列同源的β-葡萄糖苷酶（β-D-葡萄糖苷葡萄糖苷水解酶，EC 3.2.1.21），其在来自相似和不同年龄培养物的不同制备物中的相对量不同。2.纯化的高分子量物质的老化导致一定量的降解成一系列低分子量物质。3.通过凝胶过滤，从纯化的高分子量酶衍生的各种物质的粗略分子量估计为350000-3800000、170000、180000、83000-87000和45000-47000。4.负染的350000-380000分子量的酶的电子显微照片显示，该分子是八聚体，其中每个大致球形的单体占据立方体的一个角，每个边长约7.14nm。5.酶的每个分子量物质的还原形式的羧酰胺甲基化导致分子不可逆地解离成分子量为10000-12000的分子学上相同的多肽。6.这些结果表明在平衡2（4 n）在平衡4（2n）在平衡8（n）中的（8 n）类型的缓慢缔合-解离，其中n被定义为单体。该单体又由四个非催化的多肽a亚基组成。7.四种酶的米氏常数（Km）和热稳定性随分子复杂度的增加而增加，但在低浓度底物（邻硝基苯基β-D-吡喃葡萄糖苷）下，四种酶均被甘油（100 nM）抑制，而在高浓度底物下则被激活。8.只有最低分子量的物种（45种（45，000 -47000 mol.重量）显示底物抑制。
1. A homologous series of beta-glcosidase (beta-D-glcoside glcohydrolase, EC 3.2.1.21), which varied in relative amounts in different preparations from cultures of similar and different age, was observed in cultures od Botryodiplodia theobromae Pat grown for 4-8 week on cotton flock (cellulose) as carbon source. 2. Aging of the purified high-molecular-weight species led to some amount of siddociation into a homolous series of lower-molecular-weight speices. 3. Rough molecular-weight estimates, by gel filtration, of the various species derived from the purifeid high-molecular-weight enzyme were 350000-3800000, 170000, 180000, 83000-87000 and 45000-47000. 4. Electron micrographs of the negatively stained 350000-380000-molecular-weight enzyme showed that the molecule is an octamer in which each roughly spherical monomer occupies a corner of a cube with each side about 7.14nm long. 5. Carboxamidomethylation of the reduced form of each molecular-weight species of the enzyme led to irreversible dissociation of the molecules into electrophoretically identical polypeptides with a moleclar weight of 10000-12000. 6. These results suggest a slow association-dissociation of the type (8n)in equilibrium 2 (4n) in equilibrium 4(2n) in equilibrium 8(n), where n is defined as the monomer. The monomer is in turn made up of four polypeptide a subunits whi-ch are non-catalytic. 7. The Michaelis constants (Km) and heat stability of the four wnzymically active molecular species derived from the purified enzyme increased with molecular complexity, whereas all four species were inhibited by glycerol (100nM) at low concentrations of substrate (o-nitrophenyl beta-D-glucopyranoside) but activated at high substrat concentrations. 8. Only the lowest-molecular-weight species (45species (45,000-47000 mol. wt.) showed substrate inhibition.