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首页> 外文期刊>Journal of Agricultural and Food Chemistry >Conformational Study of Red Kidney Bean (Phaseolus vulgaris L.) Protein Isolate (KPI) by Tryptophan Fluorescence and Differential Scanning Calorimetry
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Conformational Study of Red Kidney Bean (Phaseolus vulgaris L.) Protein Isolate (KPI) by Tryptophan Fluorescence and Differential Scanning Calorimetry

机译：色氨酸荧光和差示扫描量热法研究红芸豆蛋白分离物（KPI）的构象

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摘要

Fluorescence and differential scanning calorimetry (DSC) were used to study changes in the conformation of red kidney bean (Phaseolus vulgaris L) protein isolate (KPI) under various environmental conditions. The possible relationship between fluorescence data and DSC characteristics was also discussed. Tryptophan fluorescence and fluorescence quenching analyses indicated that the tryptophan residues in KPI, exhibiting multiple fluorophores with different accessibilities to acrylamide, are largely buried in the hydrophobic core of the protein matrix, with positively charged side chains close to at least some of the tryptophan residues. GdnHCl was more effective than urea and SDS in denaturing KPI. SDS and urea caused variable red shifts, 2-5 nm, in the emission λ_(max), suggesting the conformational compactness of KPI. The result was further supported by DSC characteristics that a discernible endothermic peak was still detected up to 8 M urea or 30 mM SDS, also evidenced by the absence of any shift in emission maximum (λ_(max)) at different pH conditions. Marked decreases in T_d and enthalpy (AH) were observed at extreme alkaline and/or acidic pH, whereas the presence of NaCl resulted in higher T_d and AH, along with greater cooperativity of the transition. Decreases in T_a and ΔH were observed in the presence of protein perturbants, for example, SDS and urea, indicating partial denaturation and decrease in thermal stability. Dithio-threitol and N-ethylmaleimide have a slight effect on the thermal properties of KPI. Interestingly, a close linear relationship between the T_d (or ΔH) and the λ_(max) was observed for KPI in the presence of 0-6 M urea.
机译：荧光和差示扫描量热法（DSC）用于研究在各种环境条件下红芸豆（Phaseolus vulgaris L）蛋白分离物（KPI）构象的变化。还讨论了荧光数据和DSC特性之间的可能关系。色氨酸荧光和荧光猝灭分析表明，KPI中的色氨酸残基显示出对丙烯酰胺具有不同可及性的多个荧光基团，大部分被埋在蛋白质基质的疏水核中，带正电的侧链接近至少一些色氨酸残基。在使KPI变性方面，GdnHCl比尿素和SDS更有效。 SDS和尿素在发射λ_（max）中引起2-5 nm的可变红移，表明KPI的构象紧密性。 DSC特性进一步支持了该结果，即使在高达8 M的尿素或30 mM SDS的情况下，仍可检测到明显的吸热峰，这也由在不同pH条件下最大排放量（λ_（max））没有任何变化来证明。在极端的碱性和/或酸性pH下观察到T_d和焓（AH）显着降低，而NaCl的存在导致更高的T_d和AH，以及更高的跃迁协同性。在存在蛋白质扰动剂（例如SDS和尿素）的情况下，观察到T_a和ΔH降低，表明部分变性并降低了热稳定性。二硫苏糖醇和N-乙基马来酰亚胺对KPI的热性能影响不大。有趣的是，在尿素为0-6 M的情况下，对于KPI，观察到T_d（或ΔH）和λ_（最大值）之间的紧密线性关系。

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