Topic
Committed step
About: Committed step is a research topic. Over the lifetime, 6 publications have been published within this topic receiving 94 citations.
Papers
TL;DR: This report describes the first demonstration of slow-onset feedback inhibition of an enzyme that catalyzes the first committed step in a biosynthetic pathway, alpha-Isopropylmalate synthase (IPMS), which is feedback-inhibited by l-leucine.
Abstract: This report describes the first demonstration of slow-onset feedback inhibition of an enzyme that catalyzes the first committed step in a biosynthetic pathway. α-Isopropylmalate synthase (IPMS) catalyzes the first committed step of the l-leucine biosynthetic pathway and is feedback-inhibited by l-leucine. Initial velocity experiments on the Mycobacterium tuberculosis IPMS indicate that inhibition by l-leucine is linearly noncompetitive versus α-ketoisovalerate. Time-courses displayed a burst of product formation followed by a linear steady-state rate when reactions were initiated by the addition of enzyme. The burst rate showed a hyperbolic dependence on the concentration of l-leucine indicating that inhibition proceeds in two steps, an initial rapid binding step followed by slow isomerization to a more tightly bound complex.
41 citations
TL;DR: The turnover product of the committed step of menaquinone biosynthesis was isolated and determined to be (1R,2S,5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylate.
28 citations
TL;DR: The phenotypic consequences of miss-regulating the rate limiting cytochrome P450s involved in the pathway on lignin structure and quantity are described, and the flexibility of plants in channelling carbon through the phenylpropanoid grid is discussed.
Abstract: The phenylpropanoid metabolism channels carbon from phenylalanine to the three monolignols and numerous other phenolic compounds. Our understanding of the pathway has changed tremendously over the last decade, which was driven largely by the biochemical and genetic characterization of the cytochrome P450s catalysing the hydroxylation of the aromatic ring. The first, cinnamate 4-hydroxylase, is the rate-limiting step into the phenylpropanoid pathway and is highly specific for cinnamate. Blocking this step impairs the ability of plants to produce lignin. The 3-hydroxylation occurs primarily on the level of the 4-coumaroyl-shikimate level, rather than on the free acid or CoA-ester as previously expected, thereby linking the far upstream shikimate pathway with the committed step towards S and G lignin. Finally, the last hydroxylation step occurs on the level of the aldehyde or alcohol and defines flow into S lignin as indicated by mutant and over-expressing lines. Here, we summarize our current understanding of the phenylpropanoid pathway, describe the phenotypic consequences of miss-regulating the rate limiting cytochrome P450s involved in the pathway on lignin structure and quantity, and discuss the flexibility of plants in channelling carbon through the phenylpropanoid grid.
19 citations
TL;DR: It is proposed that in multi-enzyme complexes, the rate-limiting reaction need not be the first committed reaction in the sequence, which contrasts with dissociated enzyme systems in which the first commit step in a pathway is normally theRate-determining reaction.
9 citations
TL;DR: This chapter discusses the enzymatic control of pyrrole synthesis (porphobilinogen), which focuses on the mechanism of the reaction and the nature and conformation of the enzyme involved in a particular biological system.
Abstract: Publisher Summary This chapter discusses the enzymatic control of pyrrole synthesis (porphobilinogen). It focuses on the mechanism of the reaction and the nature and conformation of the enzyme involved in a particular biological system. Porphobilinogen is enzymatically synthesized (δ-aminolevulinic acid dehydratase) from two molecules of δ-aminolevulinic acid that arise from the condensation of succinyl-CoA and glycine (δ-aminolevulinic acid synthetase). The synthesis of the aminoketone, δ-aminolevulinic acid, can be considered to be the first committed step in the series of reactions that lead to the synthesis of porphyrins and related compounds, whereas the synthesis of the pyrrole is the step in which aromatization occurs. The latter reaction may also be considered a distinct committed step, because an aliphatic compound is changed into an aromatic ring compound. If these two enzymatic reactions are committed steps, they may both be subjected to metabolic control by feedback inhibition and/or by repression.
6 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2017 | 1 |
| 2012 | 1 |
| 2007 | 1 |
| 2005 | 1 |
| 1976 | 1 |
| 1968 | 1 |