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The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins. [1] A protein solution is mixed with Hopkins Cole reagent, which consists of glyoxylic acid. Concentrated sulfuric acid is slowly added to form two layers. A purple ring appears between the two ...
The structure of glyoxylic acid is shown as having an aldehyde functional group. The aldehyde is only a minor component of the form most prevalent in some situations. Instead, glyoxylic acid often exists as a hydrate or a cyclic dimer. For example, in the presence of water, the carbonyl rapidly converts to a geminal diol (described as the ...
The reaction relies on the interaction between glyoxylic acid and the indole ring of the amino acid tryptophan, a structural feature found in most proteins. When proteins are exposed to concentrated sulfuric acid and glyoxylic acid, the indole group undergoes a reaction that produces a highly colored compound.
Glyoxal was first prepared and named by the German-British chemist Heinrich Debus (1824–1915) by reacting ethanol with nitric acid. [4] [5]Commercial glyoxal is prepared either by the gas-phase oxidation of ethylene glycol in the presence of a silver or copper catalyst (the Laporte process) or by the liquid-phase oxidation of acetaldehyde with nitric acid.
This acetate, bound to the active thiol group of coenzyme A, enters the citric acid cycle (TCA cycle) where it is fully oxidized to carbon dioxide. This pathway thus allows cells to obtain energy from fat. To use acetate from fat for biosynthesis of carbohydrates, the glyoxylate cycle, whose initial reactions are identical to the TCA cycle, is ...
In a protein or peptide, these reactions are important because they may alter its structure, stability or function and may lead to protein degradation. The net chemical change is the addition of a water group and removal of an ammonia group, which corresponds to a +1 (0.98402) Da mass increase.
Glyoxylate and dicarboxylate metabolism describes a variety of reactions involving glyoxylate or dicarboxylates.Glyoxylate is the conjugate base of glyoxylic acid, and within a buffered environment of known pH such as the cell cytoplasm these terms can be used almost interchangeably, as the gain or loss of a hydrogen ion is all that distinguishes them, and this can occur in the aqueous ...
In enzymology, a glycine dehydrogenase (EC 1.4.1.10) is an enzyme that catalyzes the chemical reaction glycine + H 2 O + NAD + ⇌ {\displaystyle \rightleftharpoons } glyoxylate + NH 3 + NADH + H + The 3 substrates of this enzyme are glycine , H 2 O , and NAD + , whereas its 4 products are glyoxylate , NH 3 , NADH , and H + .