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There are two isozymes of COX encoded by distinct gene products: a constitutive COX-1 (this enzyme) and an inducible COX-2, which differ in their regulation of expression and tissue distribution. The expression of these two transcripts is differentially regulated by relevant cytokines and growth factors . [ 9 ]
Cyclooxygenase (COX), officially known as prostaglandin-endoperoxide synthase (PTGS), is an enzyme (specifically, a family of isozymes, EC 1.14.99.1) that is responsible for biosynthesis of prostanoids, including thromboxane and prostaglandins such as prostacyclin, from arachidonic acid.
The COX-3 isozyme is encoded by the same gene as COX-1, with the difference that COX-3 retains an intron that is not retained in COX-1. [1] [2] The other two cyclooxygenase isozymes are known to convert dihomo-γ-linolenic acid and arachidonic acid into prostaglandins, and are the targets of nonsteroidal anti-inflammatory drugs (NSAIDs).
The 5 isozymes of LDH Distinction between five isozymes using electrophoresis. 1.) The enzyme lactate dehydrogenase is a tetramer made of two different sub-units, the H-form and the M-form. These combine in different combinations depending on the tissue: [7]
Structure of COX-2 inactivated by Aspirin. In the active site of each of the two enzymes, Serine 516 has been acetylated. Also visible is the salicylic acid which has transferred the acetyl group, and the heme cofactor. There are at least two different cyclooxygenase isozymes: COX-1 (PTGS1) and COX-2 (PTGS2).
In cells, COX-1 and COX-2 metabolize arachidonic acid to PGH2 which is then converted to PGE2 by any one of three isozymes, PTGES, PTGES2, and PTGES3 or, alternatively, to PGD2 by either of two enzymes, a glutathione-independent synthase termed lipocalin-type Prostaglandin D2 synthase (PTGDS or L-PGDS) and a glutathione-dependent hematopoietic-type H-PGDS or PTGDS2; the COX's also metabolizes ...
A related nitric-oxide reductase (EC 1.7.99.7) exists in denitrifying species of archaea and eubacteria and is a heterodimer of cytochromes b and c. Phenazine methosulphate can act as acceptor. It has been suggested that cytochrome c oxidase catalytic subunits evolved from ancient nitric oxide reductases that could reduce both nitrogen and oxygen.
Another group discovered a novel cDNA species encoding a protein with similar structure to COX-1 while studying phorbol-ester-induced genes in Swiss 3T3 cells. The same laboratory showed that this gene truly expressed a novel COX enzyme. The two enzymes were renamed COX-1, referring to the original enzyme and COX-2. [5]