Can anyone please help me how to calculate the turnover number?
The enzyme reaction shown was performed in a 10 ml volume with a concentration of PDE5 of 0.1ug/ml. The enzyme has a molecular weight of 50000 and has one active site. Calculate the turnover numbers for PDE5 with cGMP and with cAMP as substrates.
Thanks
To calculate the turnover number of an enzyme, you need to know the rate of the enzymatic reaction and the concentration or amount of enzyme used.
The turnover number, also known as kcat, represents the number of substrate molecules converted into product molecules per unit of time at saturating substrate concentrations.
To calculate the turnover number, follow these steps:
1. Determine the amount of enzyme used in the reaction. In this case, the concentration of PDE5 is given as 0.1 μg/mL.
2. Convert the concentration of PDE5 in μg/mL to μM (micromolar). To do this, you need to know the molecular weight of PDE5. In this case, the molecular weight is given as 50,000 g/mol or 50 kDa.
- Convert 0.1 μg/mL to μM:
First, convert μg to mg: 0.1 μg = 0.0001 mg
Then, convert mg to g: 0.0001 mg = 0.0000001 g
Finally, convert g to μM using the molecular weight: 0.0000001 g × (1 mol / 50,000 g) × (10^6 μM / 1 mol) = 0.002 μM
Therefore, the concentration of PDE5 is 0.002 μM.
3. Determine the reaction rate in units of substrate molecules converted to product molecules per unit of time. The rate can be obtained experimentally by measuring the conversion of substrate to product over a specific time period.
4. Calculate the turnover number using the following formula:
kcat = (Reaction rate in molecules per unit of time) / (Enzyme concentration in moles)
Now, you can calculate the turnover number for PDE5 with cGMP and with cAMP as substrates. To perform this calculation, you will also need the reaction rate and substrate concentration for each case.
Please provide the reaction rates and substrate concentrations for PDE5 with cGMP and cAMP so that I can assist you further in calculating the turnover numbers.