fisheries science

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

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

5. • 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.

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

7. • 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.

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

10. 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.

11. 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:

12. phagocyte function are
(1) the arachidonic acid (AA) released by phospholipase
A2 (PLA2),
(2) inositol trisphosphate (IP3) 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).

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

14. MPO catalyzes the H2O2-mediated oxidation of chloride to form
HOCl, which reacts with the bacterium (yellow) or neutrophil
proteins to produce cytotoxic chloramines [monochloramine
(NH2Cl) and protein chloramine (PNHCl)].

15. •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

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

17. 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.