Enzyme Activity Units Converter

One Enzyme Unit (U) is defined as the amount of the enzyme that catalyzes the conversion of 1 micro-mole (µmol) of substrate per minute under specified conditions of temperature, pH, and substrate concentration.

The katal is the official SI unit of catalytic activity. One katal is defined as the amount of enzyme that catalyzes the conversion of 1 mole of substrate per second.

The Enzyme Unit (U) is still more widely and historically used in many biochemistry labs and commercial enzyme preparations. However, the katal (kat) is the officially recognized SI unit and is preferred by many scientific journals for standardization.

There are 60,000,000 (6 x 10⁷) Enzyme Units in one katal.

Specific activity is a measure of enzyme purity. It is defined as the units of enzyme activity per milligram of total protein (e.g., U/mg protein). A higher specific activity indicates a purer enzyme preparation.

It is often measured using a spectrophotometer to monitor the appearance of a product or disappearance of a substrate over time. If the product or substrate absorbs light, the change in absorbance can be used to calculate the reaction rate.

Vmax is the maximum initial velocity or rate of an enzyme-catalyzed reaction when the enzyme is saturated with substrate. It is directly proportional to the amount of active enzyme present.

Km is the substrate concentration at which the reaction rate is half of Vmax. It is an inverse measure of the substrate's affinity for the enzyme. A low Km indicates high affinity.

Enzymes are proteins with a specific three-dimensional structure required for activity. High temperatures can cause the enzyme to denature (unfold) and lose its activity. Low temperatures decrease the kinetic energy of molecules, slowing the reaction rate.

The amino acids in an enzyme's active site often need to be in a specific protonation state (charged or uncharged) to bind the substrate and catalyze the reaction. Extreme pH values can alter these charges and denature the enzyme, leading to a loss of activity.

An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Inhibitors are a major area of study in pharmacology and drug development.

No, not with a simple conversion factor. The relationship between temperature and enzyme activity (the Q₁₀ temperature coefficient) is complex and specific to each enzyme. Activity must be measured experimentally at the desired temperature.

It means the concentration of the substrate is high enough that all active sites of the enzyme molecules are occupied with substrate. Under these conditions, the reaction rate is limited only by how fast the enzyme can process the substrate (Vmax).

Commercial enzymes come with a Certificate of Analysis that lists the specific activity (e.g., in U/mg) and the concentration of the protein (e.g., in mg/mL). You can multiply these to get the activity concentration (e.g., in U/mL).

It can. Many enzymes are stored at -20°C or -80°C in a cryoprotectant like glycerol to prevent damage from ice crystal formation during freezing. Repeated freeze-thaw cycles should be avoided.

This is an indirect method used when the primary enzyme's reaction is difficult to monitor. The product of the first reaction is used as the substrate for a second "coupling" enzyme, whose reaction *is* easy to monitor (e.g., produces a change in color or fluorescence).

No. While clinical labs report enzyme levels (e.g., in U/L), those measurements are performed on certified analyzers under strictly controlled diagnostic protocols. This tool is for research use only.

The turnover number (kcat) is the maximum number of substrate molecules converted to product per enzyme active site per unit of time. It is calculated as kcat = Vmax / [E], where [E] is the enzyme concentration.

Concentration refers to the amount of enzyme protein in a volume (e.g., mg/mL). Catalytic activity (e.g., U/mL) refers to how effective that enzyme is at catalyzing a reaction. A solution could have a high protein concentration but low activity if the enzyme is denatured or inhibited.

Minor variations in temperature, pH, pipetting accuracy, or reagent age can all contribute to variability in enzyme assay results. Consistency is key.

No. Activity units are specific to the enzyme and the reaction it catalyzes. They are not interchangeable between different enzymes.

If the plot of product formation over time is not a straight line, it could be due to substrate depletion, product inhibition, or enzyme instability. You must use only the initial, linear portion of the curve to calculate the rate.

Enzymology can be complex. For assistance with experimental design or data interpretation, consult a biochemistry textbook, a senior researcher in your lab, or your academic supervisor.

No. To ensure your privacy, all calculations are done in your browser and no data is sent to our servers.

Indirectly. If your protocol calls for adding 5 mU of activity to a reaction, and you know the activity concentration of your enzyme stock (e.g., 1000 mU/mL), you can use the dilution formula (C₁V₁=C₂V₂) to find the volume to add.