实验教学中乳糖酶活性的测定
August 6th, 2018
乳糖酶活性对双糖乳糖的分解加工至关重要。在这里, 在膳食补充剂中发现的乳糖酶活性是用比色法测定的。这为学生提供了一个实验平台, 以了解乳糖酶的活性和酵素动力学。
这种方法是向学生介绍控制酶反应的概念的有用工具。这种技术的主要优点是它适合湿实验室经验很少的学生，为学生提供可靠的观察和解释结果。要开始实验步骤，请标记 15 mL 试管悬液。
使用研钵和研杵将一片含有 200 毫克酶的乳糖酶片剂压碎成均匀的粉末。将所得粉末放入标记的试管中，并将其重新悬浮在 10 毫升 100 毫摩尔磷酸盐缓冲盐水或 PBS 中。涡旋溶液 1 分钟，以最大程度地提取酶。
接下来，将 1 毫升从悬浮液中转移到 1.5 毫升试管中，并以 10， 000 倍 G 的速度旋转样品 1 分钟，以沉淀固体颗粒。将 500 微升上清液转移到干净的 1.5 毫升管中，标有乳糖酶提取物。将 390 微升 100 毫摩尔 PBS 放入 1.5 毫升标有反应 A 的试管中，然后加入 100 微升 5 毫摩尔 ONPG 溶液，涡旋混合均匀。
将 10 微升提取物加入反应 A 管中，涡旋内容物。通常观察反应混合物 5 分钟，并注意溶液的任何比色变化。设置两个 1.5 mL 试管，一个标记的反应 B，一个标记的对照。
向反应 B 管中加入 390 微升 100 毫摩尔 PBS，向对照管中加入 400 微升 100 毫摩尔 PBS，然后向每管中加入 100 微升 5 毫摩尔 ONPG。涡旋混合内容物。向反应 B 管中加入 10 μL 乳糖酶提取物，涡旋混合，并在室温下让反应进行 1 分钟。
一分钟后，向两根试管中加入 500 微升一摩尔碳酸钠，通过增加 pH 值来抑制乳糖酶，从而终止反应。将 500 微升从每个试管转移到干净的分光光度计比色皿中，并测量 420 纳米处的吸光度。设置三个对照管和三个反应管，并将它们标记为 4 摄氏度、室温和 37 摄氏度。
加入酶提取物后，将一管在冰上孵育，一根在室温下孵育，一根在 37 摄氏度下在预热的水浴中孵育一分钟。然后向每个试管中加入 500 微升 1 摩尔碳酸钠以终止反应。测量每根管在 420 纳米处的吸光度。
记录这些值，在每种情况下从反应值中减去控制值。使用该方案，当含有乳糖酶片剂提取物的反应溶液在 ONPG 水解时变为黄色，释放邻位硝基苯酚，对照保持澄清。使用分光光度计分析样品后，当反应在冰上孵育时，邻位硝基苯酚的产生量最低，而在 37 摄氏度下进行反应时，邻硝基苯酚的产生量最高。
在尝试此程序时，重要的是要记住在添加酶提取物之前在适当的温度下进行反应。
概述
本文介绍了一种用于测量乳糖酶酶活性的比色测定法，这对乳糖消化至关重要。该方法专为具有最少湿实验室经验的学生设计，使他们能够有效地观察和解释酶动力学。
关键研究组成部分
科学领域
- 生物化学
- 酶动力学
- 实验室技术教育
背景
- 乳糖酶是一种将乳糖分解为葡萄糖和半乳糖的酶。
- 理解酶活性在生物化学及相关领域中是基础。
- 比色测定法提供了酶反应的视觉表现。
- 这种方法适合实验室经验有限的学生。
研究目的
- 通过动手实验向学生介绍酶动力学。
- 提供一种可靠的测量乳糖酶活性的方法。
- 增强对影响酶反应因素的理解。
使用的方法
- 从膳食补充剂中制备乳糖酶提取物。
- 比色测量邻硝基苯酚生成。
- 比较不同温度下的酶活性。
- 使用分光光度法来量化吸光度变化。
主要结果
- 当邻硝基苯酚葡糖苷被乳糖酶水解时，反应混合物变黄。
- 酶活性在37摄氏度时最高，在冰上时最低。
- 对照样品保持清澈，确认了测定法的特异性。
- 结果显示了温度对酶动力学的影响。
结论
- 比色测定法有效地说明了乳糖酶活性。
- 这种方法适合生物化学教育目的。
- 理解酶动力学对未来的代谢过程研究至关重要。
常见问题解答
Executive Industry Relevance
This educational protocol demonstrates a foundational enzyme activity assay using lactase, a therapeutically relevant target in gastrointestinal disorders. The colorimetric method provides a scalable, reproducible approach for teaching enzyme kinetics principles applicable to early-stage target validation and assay development in biopharma R&D. By linking enzymatic function to a clinically significant substrate (ONPG), the assay supports mechanistic de-risking and predictive confidence in enzyme-targeted therapeutic strategies.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of lactase enzyme function and substrate specificity, supporting target hypothesis testing in gastrointestinal disease models.
- Operational Value: Uses commercially available lactase from dietary supplements, offering a low-cost, accessible system for preliminary target engagement studies.
- Predictive Value: Quantitative absorbance measurements at 420 nm allow assessment of enzyme activity under varying conditions, informing structure-activity relationships and lead candidate screening.
Screening & Assay Development
- Assay Readiness: The ONPG-based colorimetric reaction produces a quantifiable yellow product (ortho-nitrophenol), enabling high-throughput compatible readouts for enzyme inhibition or activation screening.
- Reproducibility: Standardized extraction from tablets and controlled incubation conditions (ice, room temp, 37°C) ensure consistent results across replicates, supporting assay robustness.
- Scalability: Simple tube-based format with spectrophotometric detection allows adaptation to multi-well platforms for compound library screening.
Translational & Preclinical Research
- Disease Relevance: Lactase deficiency is directly linked to lactose intolerance, making this assay a relevant tool for evaluating enzyme replacement therapies or dietary interventions.
- Translational Continuity: Temperature-dependent activity profiling (lowest on ice, highest at 37°C) mirrors physiological conditions, aiding in the prediction of in vivo enzyme behavior.
- Mechanistic De-risking: Clear differentiation between reaction and control tubes confirms assay specificity, reducing false-positive risks in downstream therapeutic validation.
Pipeline & Workflow Integration
The lactase activity assay fits within the early discovery continuum, supporting target validation through functional enzyme measurement and enabling assay development for screening campaigns focused on gastrointestinal targets.
- Discovery Biology: Measures lactase-mediated hydrolysis of ONPG to assess enzyme function, supporting biological de-risking of lactase as a therapeutic target.
- Screening: Produces quantitative, colorimetric outputs suitable for evaluating modulator effects in enzyme-focused screening workflows.
- Analytics: Spectrophotometric measurement at 420 nm provides objective data for comparing enzymatic activity across conditions, enabling data-driven hit selection.
- Translational Research: Links enzyme activity to lactose metabolism, connecting in vitro findings to clinical relevance in malabsorption disorders.
- Enterprise Reuse: Protocol uses standard lab equipment (vortex, centrifuge, spectrophotometer), facilitating broad adoption across discovery and preclinical teams.
Operational & Enterprise Impact
- Scientific Value: Provides mechanistic insight into enzyme-substrate interactions, enhancing target confidence and reducing ambiguity in early target validation.
- Operational Value: Employs robust, standardized steps (tablet extraction, centrifugation, temperature-controlled incubation) ensuring reproducibility and minimal variability.
- Strategic Value: Supports informed go/no-go decisions by delivering clear, quantitative activity data that reduces reliance on indirect or surrogate markers.
- Portfolio Impact: Enables risk-adjusted prioritization of lactase-targeted interventions based on empirical activity profiles under physiologically relevant conditions.
Implementation Considerations
- Requires basic biochemical competencies in enzyme handling, spectrophotometry, and solution preparation.
- Depends on access to a spectrophotometer capable of absorbance measurement at 420 nm and a centrifuge for supernatant clarification.
- Necessitates standardization of extract preparation and reaction timing to ensure consistent results across users and batches.
- Adaptation to other enzymes may require substrate and buffer optimization, as ONPG specificity is limited to galactosidase activity.
- pH shift via sodium carbonate addition is critical for reaction termination; incomplete quenching may affect absorbance accuracy.
