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首页> 外文期刊>International Journal of Biological Macromolecules: Structure, Function and Interactions >The contribution of ionic interactions to the conformational stability and function of polygalacturonase from A-niger
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The contribution of ionic interactions to the conformational stability and function of polygalacturonase from A-niger

机译：离子相互作用对A-niger聚半乳糖醛酸酶构象稳定性和功能的影响

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摘要

Aspergillus niger produces multiple forms of polygalacturonases with molecular masses ranging from 30 to 60 kDa. The high molecular weight polygalacturonase (61 +/- 2 kDa) from A. niger possesses a pH optimum of 4.3 and a pI of 3.9. The enzyme exhibited high sensitivity, both in terms of activity and structure, in the pH range of 4.3-7.0. The enzyme was irreversibly inactivated at pH 7.0. The enzyme is predominantly rich in parallel 0 structure. There is unfolding of the enzyme molecule between 4.3 and 7.0 resulting in irreversible loss of secondary and tertiary structure with the exposure of hydrophobic surfaces. ANS binding measurements, intrinsic fluorescence and acrylamide quenching measurements have confirmed the unfolding and exposure of hydrophobic surfaces. The midpoint of pH transition for both activity and secondary structure is 6.2 +/- 0.1. The pH-induced changes of polygalacturonase confirm the role of histidine residues in structure and activity of the enzyme. The irreversible nature of inactivation is due to the unfolding induced exposure of hydrophobic surfaces leading to association/aggregation of the molecule. Size exclusion chromatography measurements have established the association of enzyme at higher pH. Urea induced unfolding measurements at pH 4.3 and 7.0 have confirmed the loss in stability as we approach neutral pH. (c) 2005 Elsevier B.V. All rights reserved.
机译：黑曲霉产生多种形式的多聚半乳糖醛酸酶，其分子质量为30至60 kDa。来自黑曲霉的高分子量聚半乳糖醛酸酶（61 +/- 2kDa）具有最适pH为4.3和pI为3.9。该酶在pH范围为4.3-7.0时，在活性和结构方面均显示出高灵敏度。该酶在pH 7.0下不可逆地失活。该酶主要富含平行0结构。酶分子在4.3和7.0之间展开，导致疏水表面暴露导致二级和三级结构不可逆地损失。 ANS结合测量，固有荧光和丙烯酰胺淬灭测量已经证实疏水表面的展开和暴露。活性和二级结构的pH转换中点均为6.2 +/- 0.1。 pH诱导的聚半乳糖醛酸酶的变化证实了组氨酸残基在酶的结构和活性中的作用。灭活的不可逆性质是由于疏水表面的展开诱导暴露导致分子的缔合/聚集。尺寸排阻色谱测量已确定了较高pH下酶的缔合。在我们接近中性pH值时，尿素在pH 4.3和7.0引起的解折叠测量结果证实了稳定性的损失。 （c）2005 Elsevier B.V.保留所有权利。

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