Name: substrate effects on enzyme rates
Uploaded: 2019-08-01T09:12:17.000Z
Duration: 1 min 19 s
Channel: JoVE

بداخل الخلية الظروف البيئية المختلفة مثل تركيز المادة الأولية يمكن أن تؤثر بشكل كبير على معدل تحفيز الإنزيمات لتفاعلات كيميائية معينة هذه العملية تسمى بحركية الإنزيمات ويمكن تمثيلها على الرسم البياني بمعدل التفاعل على المحور Y والظروف المتباينة وهي تركيز المادة الأولية بهذا المثال على المحور X معدل التفاعل هو المعدل الذي يتم به تكوين المنتج ويمكن أن يصل لأقصى سرعة له والتي تعرف بـV max ويصل لمرحلة الاستقرار عندما تكون كل الإنزيمات المتاحة متحدة مع المادة الأولية لذا ما يحدد معدل التفاعل. هو تركيز الإنزيمات المتاحة لعملية الاتحاد أو الاندماج هذا الرسم البياني يمكن أن يظهر لنا معدل سرعة ارتفاع معدل زيادة التفاعل يمثل المتغير بالرمز Km أي تركيز المادة الأولية في منتصف السرعة القصوى والذي يمثل انجذاب الإنزيم إلى. أو ميله للاتحاد مع المادة الأولية الإنزيم بمعدل سرعة تفاعل Km عالية له قابلية انجذاب أكثر لأنه يصل إلى أقصى معدلاته سرعة التفاعل في تركيز قليل للمادة الأولية وبالتالي معدل زيادة سرعة تفاعل الزائد يقابل الانجذاب المنخفض لأن الإنزيم يتطلب تركيز عالي للمادة الأولية لكي يصل تفاعله لأقصى معدلاته.

جونسون ، كينيث أ. "قرن من التحليل الحركي للإنزيم ، من 1913 إلى 2013". رسائل FEBS 587 ، رقم 17 (2 سبتمبر 2013): 2753-66. [<a href = "https://doi.org/10.1016/j.febslet.2013.07.012" >مصدر</a>]
سواريز ، آر كي ، جي إف ستابلز ، جي آر بي لايتون ، وتي جي ويست. "العلاقات بين قدرات التدفق الأنزيمي ومعدلات التدفق الأيضي: التفاعلات غير المتوازنة في تحلل السكر في العضلات". وقائع الأكاديمية الوطنية للعلوم بالولايات المتحدة الأمريكية 94 ، العدد 13 (24 يونيو 1997): 7065-69. [<a href = "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC21285/.">مصدر</a>]

حركية الإنزيم

Enzyme Kinetics

تعمل الإنزيمات على تسريع التفاعلات عن طريق خفض طاقة التنشيط للمواد المتفاعلة. تسمى السرعة التي يحول بها الإنزيم المواد المتفاعلة إلى نواتج معدل التفاعل. هناك عدة عوامل تؤثر على معدل التفاعل ، بما في ذلك عدد المواد المتفاعلة المتاحة. حركية الإنزيم هي دراسة كيف يغير الإنزيم معدل التفاعل.

يدرس العلماء عادةً حركية الإنزيم بكمية ثابتة من الإنزيم في البيئة الخاضعة للتحكم في أنبوب الاختبار. عندما يتم إضافة المزيد من المواد المتفاعلة أو الركيزة إلى كمية ثابتة من الإنزيم ، يزداد معدل التفاعل حيث يمكن للإنزيم إنتاج المزيد من المنتج. نتيجة لذلك ، عندما يتم رسم معدل التفاعل مقابل تركيز الركيزة ، فإن زيادة الركيزة تزيد من معدل التفاعل. ومع ذلك ، بمجرد احتلال جميع المواقع النشطة للإنزيم ، فإن معدل التفاعل يهدأ. يسمى تركيز الركيزة التي يقوم بالوصول إلى الحد الأقصى لمعدل التفاعل Vmax. عدد جزيئات الإنزيم الحالية يحد من Vmax. في حالة زيادة كمية الإنزيم ، يزيد Vmax ، ولكن إضافة المزيد من الركيزة ليس له أي تأثير.

يمكن أن يكشف الرسم البياني لمعدل التفاعل مقابل تركيز الركيزة عن خصائص مهمة أخرى لحركية الإنزيم. يسمى تركيز الركيزة الذي يكون عنده معدل التفاعل في منتصف الطريق إلى Vmax (أي ، ١/٢ Vmax) ثابت ميكايليس (Km). Km هو تمثيل للقابلية بين الإنزيم والركيزة. الإنزيمات ذات Km الأقل تحتاج كمية أقل من الركيزة للوصول إلى Vmax وبالتالي يكون لها تقارب أعلى مع الركيزة الخاصة بها. ومن المثير للاهتمام ، بالنسبة للعديد من الإنزيمات ، أن قيمة Km قريبة جداً من التركيز الخلوي للركيزة. بالقرب من Km ، يمكن أن تؤثر التغييرات الطفيفة في تركيز الركيزة بشكل كبير على معدل التفاعل ، لذلك يمكن أن تؤثر التغييرات الصغيرة في توفر الركيزة الخلوية على وظيفة المسار البيولوجي بأكمله.

لا تنتج جميع الإنزيمات الرسم البياني لمعدل الركيزة على شكل زائدي والمعروف باسم حركية ميكايليس مينتين. تفترض حركية ميكايليس مينتين أن الإنزيم يحفز ركيزة واحدة. تحتوي الإنزيمات التي يتم تنظيمها بشكل تفارغي على مواقع نشطة متعددة وتميل إلى إنتاج رسم بياني على شكل سيني عندما يتم رسم معدل التفاعل مقابل تركيز الركيزة.

تعمل الإنزيمات على تسريع التفاعلات عن طريق خفض طاقة تنشيط المواد المتفاعلة. تسمى السرعة التي يحول بها الإنزيم المواد المتفاعلة إلى منتجات ...

Education

JoVE Core

Biology

علم الأحياء

Cellular Processes

العمليات الخلوية

Metabolism

عملية التمثيل الغذائي (الأيض)

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

substrate effects on enzyme rates

Enzyme kinetics examines how enzymes change the rate of a reaction. Enzymes speed reactions by lowering the activation energy of the reactants. The reaction rate is the speed at which an enzyme turns reactants into products, and it can be affected by several factors, including the number of available reactants.

Scientists often study enzyme kinetics in a test tube with a fixed amount of enzyme. When more substrate, or reactant, is added, the reaction rate increases because the enzyme can make more product. If the reaction rate is graphed against substrate concentration, the curve rises as substrate increases.

The rate does not keep rising forever. Once all of the enzyme's active sites are occupied, the reaction rate levels off. The substrate concentration at which the maximum rate is reached is called V max. V max is limited by the number of enzyme molecules present. If more enzyme is added, V max increases, but more substrate alone has no further effect.

A rate-versus-substrate graph can also show other features of enzyme behavior. The substrate concentration at which the reaction rate is halfway to V max is called the Michaelis constant, or K m. K m shows the affinity between an enzyme and its substrate. A lower K m means less substrate is needed to reach V max, so the enzyme has a higher affinity.

For many enzymes, K m is close to the substrate concentration in cells. Near K m, even small changes in substrate concentration can strongly affect the reaction rate. That means small shifts in cellular substrate availability can influence the activity of an entire biological pathway.

Not all enzymes follow Michaelis Menten kinetics. This model assumes that an enzyme acts on a single substrate. Enzymes regulated allosterically have multiple active sites and usually produce a sigmoid-shaped graph instead of a hyperbolic one when reaction rate is plotted against substrate concentration.

Substrate Effects on Enzyme Rates

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key terms and concepts

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Substrate Effects on Enzyme Rates | JoVE K12

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Substrate Effects on Enzyme Rates

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