A friend of yours has just returned from a nearly disastrous African safari. Whi

Question

A friend of yours has just returned from a nearly disastrous African safari. While crossing the Limpopo River, she was bitten by a poisonous water snake and nearly-died from extensive hemolysis (ie, lysis of red blood cells.) A true biologist at heart, your friend captured the snake before passed out; she has asked you to analyze the venom to discover the basis of its hemolytic activity. You find that the venom contains a protease (which breaks peptide bonds in proteins), a neuraminidase (which removes sialic acid residues from gangliosides-cleaves glycoproteins), and a phospholipase (which cleaves bonds in phospholipids). Treatment of isolated red blood cells with these purified activities gave the results shown in the table below, Analysis of the products of hemolysis produced by phospholipase treatment showed an enormous increase in free phosphorylcholine (choline with a phosphate group attached) and diacylglycerol (glycerol with two fatty acid chains attached). What is the substrate for the phospholipase, and where is it cleaved? In light of what you know of the structure of the plasma membrane, explain why ph causes lysis the of the red blood cells, the protease and neuraminidase do not

Explanation / Answer

1. The substrate for phospholipase is phopholipids mainly phosphotidyl choline. There are 4 types of phospholipase each cleave at specific sites

Here phospholipase C cleaves the phophotidylcholine.

2. Red blood cell contains phospholipids and gets affected by similar phopholipids on the plasmamembrane. But the action of phospholipase on RBC disrupts the integrity of the cell releasing the hemoglobin and thus causing hemolysis. Hence phopholipase causes hemolysis but not neuroaminadase and protease.

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