Pharmacology and chemistry of cyclooxygenase enzyme


PGG2/H2 synthase stands for ProstaGlandin G2/H2 synthase. As the name suggests it is an enzyme that belongs to the household of myeloperoxidases1 involved in synthesizing biochemical precursors. Those precursors belong to a group of eicosanoids: prostaglandin G2 ( PGG2 ) and its decreased signifier prostaglandin H2 ( PGH2 ) ( Fig.1 ) . The 2nd of these two precursors is necessary for the production of prostanoids: prostaglandins ( PGs – E2, F2, D2 ) , tromboxane A2 ( TXA2 ) and prostacyclins ( PGI2 ) . PGG2/H2 synthase stands besides for an enzyme traditionally called Cox ( COX ) ; the chief mark for pharmacological agents – COX inhibitors in the intervention of human diseases.

A heme-containing COX enzyme is a bifunctional biocatalyst with two interrelated cellular activities: Cox for endogenous substrate arachidonic acid ( AA ) and peroxidase for hydroperoxy endoperoxide ( PGG2 ) ; for concluding merchandise of hydroxy endoperoxide ( PGH2 ) ( Fig.1 ) . COX is a subdued i.e. it has two indistinguishable fractional monetary units within the construction ( a homodimer ) therefore for the enzyme to transport out both reactions with dependence of one to another, the construction possesses two braces of active sites: Cox ( COX ) and peroxidase ( POX ) per fractional monetary unit. The peroxidase active site activates the haem groups ( two per enzyme ) located in the Cox active site before the reactions take topographic point. Although these active sites are distinguishable biocatalysis of both of them is executable.

The first map involves use of molecular O with hydroperoxide moving as a beginning of it and therefore instigator of Cox activity. At C11 of AA attractive force of H by Tyr385 signifiers pentadienyl extremist that allows organizing reactive species upon fond regard of molecular O which so forms cyclic peroxide with C9 followed by 2nd formation of the span between C8 – C12 ( formation of bicyclic peroxide ) . C15 peroxyl formed ( pre-PGG2 ) utilizing following available molecule of O ( acyclic peroxide formation ) is so reduced utilizing the same H that was attracted by Tyr385 at the start of contact action therefore renewing enzyme ‘s activity for the following rhythm in prostanoids biogenesis. As a consequence formation of hydroperoxy endoperoxide – PGG2 ( cyclooxygenation or COX reaction ) is achieved ( Fig. 2 ) . The following measure so involves decrease of 2 negatrons from the PGG2 formed bring forthing PGH2 ( hydroxy endoperoxide ) , an intoxicant with a hydroxyl group created at C 15 ( peroxidase or POX reaction ) .

Chemical reaction with molecular O is a really unusual instance since in casualty it yields really reactive species i.e. groups. Since each biogenesis of PGs occurs in each nucleated cell, except lymph cell ( Tyrrell talk ) , engagement of molecular O2 is really utmost. In order to find beginning of each O atom in the construction of PGG2 an experiment utilizing an isotopic mixture of molecular O was used ( O216 and O218 ) . Such atom labelling allowed following the presence of it and finding its stairss in the formation of free groups. As a effect either isotopic molecule did non disassociate during cyclooxygenation and/or alternatively was preserved prior to cyclisation. The staying isotopic molecular O took portion peroxidising the C15. The dual diooxygenation therefore allowed for probe of hydroperoxy endoperoxide ( PGG2 ) formation followed by the decrease of it to hydroxy endoperoxide ( PGH2 ) severally. Finally, PGH2 formed gets so converted to the figure of its enzymatic derived functions ( isomerases, synthases, reductases ) required for attendant production of biologically active 2nd couriers: I2, E2, F2, D2 and tromboxane A2 6.

Mammalian cell possesses two isoforms of COX: 1 and 2. Cox 1 and COX 2 are of the same type of enzyme in respect to mechanism of action, protein folding, structural features and map. However attending must be paid when taking closer expression at them since chemical ways of structural word picture revealed several similarities and differences with some holding more importance than the others. To such chemical ways EPR spectrometry ( sensing of odd negatrons ) , crystallography, steady-state kinetic checks merely to call a few, were taken into consideration. The full appraisal is provided in the tabular array shown below ( Fig.3. ) – for more in deepness inside informations please mention to the mentions used denoted by Numberss at each subheading under “ belongings ” .

The nature of Cox suppression in the human organic structure

Mammalian cell possesses two isoforms of PGG2/H2 synthase: 1 and 2. First subtype is referred to as “ the good 1 ” whereas the 2nd as “ the bad 1 ” 3. Such general and instead simplistic word picture is due to the map of prostaglandins formed by COX-1 and 2 severally. Both isozymes have protective and invasive belongingss. To protective 1s we could rank gastro-intestinal epithelial unity, nephritic Na balance, ordinance and development of kidneys, angiogenesis and myocardial protection. The invasive nevertheless include platelet synthesis and thrombus formation, coronary artery disease, febrility, redness and its symptoms, and pain 3. Although the last two are of non desired effects however they do represent protective map every bit good as they allow for acknowledgment of something that requires our attending and therefore medical intercession. Inhibition of either action would let an upstream or downstream displacement of maps performed by each isoform.

Inhibition of Cox action is desired in the intervention of human diseases. Not merely because it suppresses the inflammatory production of prostaglandins in the conditions such as: dysmenorrhoea, arthritic arthritis, degenerative arthritis but besides because it prevents platelet collection, suppresses tumour growing and supports bone healing.

Current developments in field of COX suppression involves several agents with ability to command action of isozymes nevertheless recent restriction of their usage due to several studies of unsought side effects they cause an attack to identification their targeting is limited.

The types of Cox inhibitors in the intervention of human diseases

NSAIDs act by interfering with Cox tract which mediates production of chemicals responsible for assorted responses within the organic structure such as redness, stomachic protection and cardiovascular effects 5. Since COXes exist in two isoforms nonsteroidal anti-inflammatories can interfere with either first, 2nd or both actions at the same time.


The epoch of nonsteroidal anti-inflammatories begun at the terminal of nineteen century. It was non know until 74 old ages after the mechanism of action of cyclooxygenase inhibitor, acetylsalicylic acid, was appreciated.


  1. Comparison of the belongingss of prostaglandin Hsynthase-1 and -2. R.J. Kulmacz, W.A. new wave der Donk and A.-.L. Tsai, Progress in Lipid Research. 42 ( 2003 ) , pp. 377-404.
  2. Structural and functional differences between Coxs: Fatty acid oxygenases with a critical function in cell signalling Carol A. Rouzer, Lawrence J. Marnett Biochemical and Biophysical Research Communications 338 ( 2005 ) 34-44
  3. Progresss in the pathophysiology of constituent and inducible Coxs: two enzymes in the limelight Luca Parente and Mauro Perretti Biochemical Pharmacology Volume 65, Issue 2, 15 January 2003, Pages 153-159
  4. Prostaglandin H synthase: Resolved and unsolved mechanistic issues. Ah-Lim Tsai and Richard J. Kulmacz Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA Received 8 July 2009 ; revised 25 August 2009. Available on-line 1 September 2009.
  5. The Cyclooxygenase: Past, nowadays and hereafter. A testimonial to John R. Vane ( 1927-2004 ) . Regina M. Botting Journal of Thermal Biology 31 ( 2006 ) 208-219
  6. J Pharm Pharmaceut Sci ( World Wide Web. ) 11 ( 2 ) : 81s-110s, 2008 81s Development of Nonsteroidal Anti-Inflammatory Drugs ( NSAIDs ) : Cyclooxygenase ( COX ) Inhibition and Beyond P. N. Praveen Rao1 and Edward E. Knaus2.

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