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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.
A step with a high flux control coefficient means that changing the activity of the step (by changing the expression level of the enzyme) will have a large effect on the steady-state flux through the pathway and vice versa. Historically the concept of the rate-limiting steps was also related to the notion of the master step. [4]
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 ...
14629 Ensembl ENSG00000001084 ENSMUSG00000032350 UniProt P48506 P97494 RefSeq (mRNA) NM_001498 NM_001197115 NM_010295 RefSeq (protein) NP_001184044 NP_001489 NP_034425 Location (UCSC) Chr 6: 53.5 – 53.62 Mb Chr 9: 77.66 – 77.7 Mb PubMed search Wikidata View/Edit Human View/Edit Mouse Glutamate–cysteine ligase catalytic subunit is an enzyme that in humans is encoded by the GCLC gene ...
CTP (cytidine triphosphate) synthetase catalyzes the last committed step in pyrimidine nucleotide biosynthesis: [3] ATP + UTP + glutamine → ADP + P i + CTP + glutamate . It is the rate-limiting enzyme for the synthesis of cytosine nucleotides from both the de novo and uridine salvage pathways.
As an example, consider the gas-phase reaction NO 2 + CO → NO + CO 2.If this reaction occurred in a single step, its reaction rate (r) would be proportional to the rate of collisions between NO 2 and CO molecules: r = k[NO 2][CO], where k is the reaction rate constant, and square brackets indicate a molar concentration.
Cholesterol 7 alpha-hydroxylase is the rate-limiting enzyme in the synthesis of bile acid from cholesterol via the classic pathway, catalyzing the formation of 7α-hydroxycholesterol. The unique detergent properties of bile acids are essential for the digestion and intestinal absorption of hydrophobic nutrients. [8]
CTP:phosphocholine cytidylyltransferase (CCT), the rate-limiting enzyme of the pathway, is a nuclear/cytosolic enzyme and catalyzes the following reaction: [1]: 422 phosphocholine + CTP ⇌ CDP-choline + PP i; CCT functions as a dimer of either α and β subunits encoded by Pcyt1a and Pcyt1b, respectively.