Phago oxygen indepenedent killing mechanism

fisheries science

1. PHAGOCYTOSIS- OXYGEN INDEPENDENT KILLING MECHANISM PRESENTED BY R.PRATHISHA MFT16087(AAH)

2. Oxygen-independent activity Lysosomal granules contain a variety of extremely basic proteins that strongly inhibit bacteria, yeasts and even some viruses.

3. A few molecules of any one of these cationic proteins appear able to inactivate a bacterial cell by damage to their permeability barriers, but their exact modes of action are not known.

4. The lysosomal granules of neutrophils contain lactoferrin , an extremely powerful iron-chelating agent , which withholds potential iron needed for bacterial growth.

5. The pH of the phagolysosome may be as low as 4.0 due to accumulation of lactic acid, which is sufficiently acidic to prevent the growth of most pathogens.

6. This acidic environment apparently optimizes the activity of many degradative lysosomal enzymes including lysozyme , glycosylases , phospholipases , and nucleases.

7. Bacterial glycolipids . Glycosyl diglycerides in gram-positive bacteria. Glycosylases   are  enzymes that hydrolyze  glycosyl compounds. In turn, glycosylases are divided into two groups:  glycosidases - - enzymes that hydrolyze O- and S- glycosyl compounds -- and enzymes that hydrolyze N- glycosyl compounds.

8. A  phospholipase  is an enzyme that hydrolyzes  phospholipids [1]  into  fatty acids  and other  lipophilic  substances. There are four major classes, termed A, B, C and D, distinguished by the type of reaction which they catalyze:

9. phagocyte function are the arachidonic acid (AA) released by phospholipase A 2  (PLA 2 ), ( 2) inositol trisphosphate (IP 3 ) released by phosphatidylinositol -specific phospholipase C (PI-PLC), and (3 ) diacylglycerol (DAG) produced directly by PI-PLC or by the sequential action of phospholipase D (PLD) and phosphatidate phosphohydrolase (PAP) on phosphatidylcholine (PC).

10. In contrast to these compounds which support phagocytosis , the ceramide product of sphingomyelinase may provide a brake, inhibiting PLD and terminating ingestion.

11. MPO catalyzes the H 2 O 2 -mediated oxidation of chloride to form HOCl , which reacts with the bacterium (yellow) or neutrophil proteins to produce cytotoxic chloramines [ monochloramine (NH 2 Cl) and protein chloramine ( PNHCl )].

12. In addition, activated macrophages produce a group of antimicrobial and cytotoxic peptides, commonly known as defensins . Cathepsin G is an example for defensins . These molecules are cysteine -rich cationic peptides containing 29–35 amino-acid residues. Each peptide, which contains six invariant cysteines , forms a circular molecule that is stabilized by intramolecular disulfide bonds. DEFENSINS

13. These circularized defensin peptides have been shown to form ion-permeable channels in bacterial cell membranes.

14. Defensins can kill a variety of bacteria, including  Staphylococcus aureus , Streptococcus pneumoniae , Escherichia coli, Pseudomonas aeruginosa ,  and  Haemophilus influenzae .  Exocytosis :     Finally the killed organisms are digested by hydrolytic enzymes and the degraded products are released to the exterior by the process of exocytosis .

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