Phospholipid, short-chain

We have now extended these studies to synthetic phospholipids that contain short chain fatty acyl groups and which are water soluble, such as dibutyryl and dihexanoyl phosphatidylcholine (PC). These phospholipids are monomeric below their critical micelle concentration (cmc), yet activate the enzyme. In order to carry out kinetic studies, the long chain phospholipid substrate must generally be solubilized by a detergent such as Triton X-100 which serves as an inert matrix. Further understanding of the mechanism of the activation by short-chain phospholipids requires first a quantitation of the solubilization of these compounds by detergent ... 

Hauser, H. (2000), Short-chain phospholipids as detergents, Biochim. Biophys. Acta, 1508,164-181. 

Zhou, C., and Roberts, M.F., 1998, Nonessential activation and competitive inhibition of bacterial phosphatidylinositol-specific phospholipase C by short-chain phospholipids and analogues. Biochemistry 37 16430-16439. 

An important observation was made in the de Haas laboratory in Utrecht, where the activities of the pancreatic phospholipase and its proenzyme on the same substrate have been tested (22). The phospholipase hydrolyzes substrates that are part of a micelle, but the prophospholipase is completely inactive against micelles. The phospholipase can also hydrolyze short chain phospholipids that are in monomolecular solution although at much slower rates. The prophospholipase is almost as active as the enzyme against such substrates. It must be concluded that the reactive site of the phospholipase is already completely assembled and active in the proenzyme. Tryptic activation forms a new site that binds to micelles. This site is called the anchoring site or recognition site (22). 

Topical pancreatic lipase substrates like tributyrin and triolein emulsions are hydrolyzed by carboxylester lipase in the presence of bile salt but slowly—at a rate lower than 3% and 0.5%, respectively, of that observed with the lipase-colipase complex. On the other hand, the positional specificity is not restricted all three sn positions of triglycerides can be split by the carboxylester lipase. While long-chain phospholipids are resistant, short-chain phospholipids are readily attacked by carboxylester lipase [40]. The low substrate specificity of carboxylester lipase makes possible an essential role for this enzyme in the hydrolysis of triglycerides containing certain esterified polyunsaturated fatty acids, such as eicosapentaenoic, arachidonic, or linoleic acids [41], and which may be resistant to attack by pancreas lipase (see p. 190). 

Influence of Short Chain Phospholipid Spacers on the Properties of Diacetylenic Phosphatidylcholine Bilayers 239... 

IMFLUEilCE OF SHORT CHAIN PHOSPHOLIPID SPACERS ON THE PROPERTIES OF DIACETTLENIC PHOSPHATIDYLCHOLINE BILAYERS... 

The partition coefficient K was found to be 40 at 50 mM Triton X-100 and varied somewhat with Triton concentration (Pluckthun and Dennis, 1981). The chemical shift of the short-chain phospholipids incorporated into mixed micelles approaches that of long-chain normal phospholipids in the micelles, suggesting similar structures for the mixed micelles. 

Interestingly, Bums et al. (1983) have reported that micelles formed by short-chain phospholipids can themselves be used as deteigents to solubilize triglycerides containing short fatty chains to form microemulsion particles in which the P-NMR linewidths are narrower than for the pure phospholipid micelles. These particles serve as models for lipoproteins. 

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