Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Lipid Metabolism
Phospholipid Metabolism
Degradation and Turnover of Phospholipids

It is well known that protein molecules undergo complete degradation in Tissues. Therefore, a turnover rate can be determined for protein molecules. Phospholipids also actively break down in tissues, but the turnover rate varies for different PARTS OF THE molecule. For example, the turnover time of the phosphate group differs from that of the 1-acyl group. This is due to the presence of Enzymes that catalyze the partial Hydrolysis of phospholipids, which can be followed by their resynthesis (Fig. 11.7).

Unfortunately, comprehensive data on the phospholipase profile of various tissues are currently lacking. It is well established that phospholipase A₁ attacks the ester bond of phospholipids at position 1. Phospholipase A₂ catalyzes the hydrolysis of the ester bond at position 2 of Glycerophospholipids, yielding a free Fatty acid and a lysophospholipid (lysolecithin in the case of phosphatidylcholine), which is then re-acylated by acyl-CoA in the presence of acyltransferase.

Phospholipase C attacks the ester bond at position 3, resulting in The formation of a 1,2-diglyceride and a phosphoryl base.

Phospholipase D catalyzes the Cleavage of the nitrogenous base from the phospholipid. For a long time, it was believed that phospholipase D was exclusively present

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Fig. 11.7. Hydrolytic cleavage of specific phospholipid bonds by phospholipases.

in plant tissues. Recently, it has been detected in the soluble fraction of rat Brain, subsequently in brain and other organ microsomes, and most recently in rat Liver Cell/35.html">Mitochondria.

The status of phospholipase B remains unclear. It may represent a mixture of enzymes possessing The properties of both phospholipase A₁ and A₂. Alternatively, phospholipase B could be an enzyme specific for lysophospholipids (e.g., lysolecithin), functioning essentially as a lysophospholipase.