Enzyme Catalytic Efficiency
Enzyme Catalytic Efficiency - Related Videos
01:07
Catalytically Perfect Enzymes
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2023
The theory of catalytically perfect enzymes was first proposed by W.J. Albery and J. R. Knowles in 1976. These enzymes catalyze biochemical reactions at high-speed. Their catalytic efficiency values range from 108-109 M-1s-1. These enzymes are also called 'diffusion-controlled' as the only rate-limiting step in the catalysis is that of the substrate diffusion into the active site. Examples include triose phosphate isomerase, fumarase, and superoxide dismutase. Most enzymes achieve catalytic...
01:19
Turnover Number and Catalytic Efficiency
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2023
The turnover number of an enzyme is the maximum number of substrate molecules it can transform per unit time. Turnover numbers for most enzymes range from 1 to 1000 molecules per second. Catalase has the known highest turnover number, capable of converting up to 2.8×106 molecules of hydrogen peroxide into water and oxygen per second. Lysozyme has the lowest known turnover number of half a molecule per second. Chymotrypsin is a pancreatic enzyme that breaks down proteins during digestion. The...
02:34
Enzymes
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2020
Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the activation energies of biochemical reactions by forming complexes with its substrates. The lowering of activation energies favor an increase in the rates of biochemical reactions. Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD...
08:56
Catalytic Reactor: Hydrogenation of Ethylene
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2023
Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA The hydrogenation of ethylene (C2H4) to ethane (C2H6) has often been studied as a model reduction reaction in characterizing new metal catalysts.1-2 While supported nickel is not the most active metal catalyst for this reaction, it is active enough that reaction can take place at < 200°C. The reaction typically involves adsorbed, dissociated hydrogen (H2) reacting...
08:07
Enzyme Assays and Kinetics
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2023
Enzyme kinetics describes the catalytic effects of enzymes, which are biomolecules that facilitate chemical reactions necessary for living organisms. Enzymes act on molecules, referred to as substrates, to form products. Enzyme kinetic parameters are determined via assays that directly or indirectly measure changes in substrate or product concentration over time. This video will cover the basic principles of enzyme kinetics (including rate equations) and kinetic models. The concepts governing...
FAQs
At low substrate concentrations, kcat/Km is useful because it combines two kinetic features into one comparative value. kcat captures how many substrate-to-product reactions an enzyme completes per unit time, whereas Km represents the substrate concentration associated with the reaction rate. Their ratio therefore helps assess performance when substrate is scarce, rather than describing turnover alone.
An enzyme can have a high turnover value without having the highest catalytic efficiency. Because kcat/Km incorporates both turnover and the Km-related substrate response, comparing kcat alone may miss differences in apparent substrate affinity. This distinction is important when evaluating enzymes or variants under low-substrate conditions, where the combined specificity constant is more informative than either component considered separately.
Changes in pH or temperature can alter the measured catalytic efficiency, so comparisons should account for environmental conditions. A value obtained under one condition may not represent the same enzyme’s performance under another. Testing these variables helps determine whether an observed difference reflects the enzyme itself, such as a mutation, or the surrounding conditions in which catalysis occurs.
To quantify catalytic efficiency, investigators determine the kinetic quantities kcat and Km and use their ratio, kcat/Km, as the specificity constant. The resulting value can then be compared across enzymes, mutations, or tested conditions. This approach turns reaction-rate measurements into a metric that supports direct evaluation of catalytic performance, particularly at low substrate concentrations.
Enzyme catalytic efficiency is especially useful for comparing a parent enzyme with a mutant or for examining how an enzyme fits into a metabolic pathway. Differences in the specificity constant can reveal altered catalytic performance and help researchers evaluate enzyme evolution. The same comparison framework also supports biotechnology, where catalytic behavior is relevant to selecting or improving biological catalysts.
In drug design, catalytic-efficiency measurements can help compare enzyme forms and characterize changes in catalytic behavior that matter for biological targets. The metric is also useful when connecting molecular changes to function, because it incorporates both reaction completion rate and apparent substrate affinity. Thus, it provides a broader basis for interpretation than considering reaction speed alone.