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In biochemistry, a rate-limiting step is a reaction step that controls the rate of a series of biochemical reactions. [1] [2] The statement is, however, a misunderstanding of how a sequence of enzyme-catalyzed reaction steps operate. Rather than a single step controlling the rate, it has been discovered that multiple steps control the rate.
In the simplest case the initial step is the slowest, and the overall rate is just the rate of the first step. Also, the rate equations for mechanisms with a single rate-determining step are usually in a simple mathematical form, whose relation to the mechanism and choice of rate-determining step is clear.
In normal usage, the rate-limiting step or rate-determining step is defined as the slowest step of a chemical reaction that determines the speed (rate) at which the overall reaction proceeds. The flux control coefficients do not measure this kind of rate-limitingness. For example, in a linear chain of reactions at steady-state, all steps carry ...
Most enzymes have a rate around 10 5 s −1 M −1. The fastest enzymes in the dark box on the right (>10 8 s −1 M −1) are constrained by the diffusion limit. (Data adapted from reference [1]) A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or ...
The first step and the rate-limiting step of lipolysis is carried out by adipose triglyceride lipase (ATGL). This enzyme catalyzes the hydrolysis of triacylglycerol to diacylglycerol . Subsequently, hormone-sensitive lipase (HSL) catalyzes the hydrolysis of diacylglycerol to monoacylglycerol and monoacylglycerol lipase (MGL) catalyzes the ...
The cytosolic acetyl-CoA can be carboxylated by acetyl-CoA carboxylase into malonyl CoA, the first committed step in the synthesis of fatty acids, or it can be combined with acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA which is the rate limiting step controlling the synthesis of cholesterol. [47]
The observed rate of chemical reactions is, generally speaking, the rate of the slowest or "rate determining" step. In diffusion controlled reactions the formation of products from the activated complex is much faster than the diffusion of reactants and thus the rate is governed by collision frequency .
This step of the reaction whose rate determines the overall rate of reaction is known as rate determining step or rate limiting step. The height of energy barrier is always measured relative to the energy of the reactant or starting material.