Glycerophosphatides degradation

This discussion will be confined to a general description of the biosynthesis and degradation of the glycerophosphatides commonly found in animal tissues. Reference will be made to the glycerophosphatides of plants and bacteria for comparative purposes only. Even with these severe restrictions, it will be possible to refer to no more than a small selection of the many important papers that have appeared on the subject during the past few years. 

Enzymes capable of degrading glycerophosphatides are found in snake venoms, plants and bacteria. It is only recently, however, that the presence of many of these enzymes has been established beyond question in animal tissues, for in much of the earlier work bacterial contamination was not adequately controlled. 

It is highly hkely that phosphatidyl serine is broken down in animal tissues by a series of reactions similar to those already described for lecithin and phosphatidyl ethanolamine. Both phosphalipase A (Long and Penny 1957) and phospholipase B (Fairbairn 1948) remove fatty acids from serine glycerophosphatides. Also phospholipase C is reported to be inactive (MacFarlane 1948, Zamecnik et al. 1947), whereas phospholipase D degrades phosphatidyl serine into free serine and phosphatidic acid (Kates 1956). 

Phosphatidyl inositol may be degraded by one of two pathways. Dawson (1959) showed that an enzyme preparation from P. notatum breaks down phosphatidyl inositol by a series of reactions analogous to those catalysed by phospholipase A (Reaction 35) phospholipase B or lysophosphofipase (Reaction 36) GPC-diesterase (Reaction 39) and phosphomonoesterase (Reaction 40). Kemp, Hub-SCHER and Hawthorne (1961) reported a similar degradation of phosphatidyl inositol by a rat fiver enzyme preparation. The fiver enzyme does not attack lecithin or any of the other glycerophosphatides, whereas the P. notatum enzyme of Dawson (1959) hydrolyses lysolecithin. 

Thus phosphatidyl inositol may be broken down by enzymes similar to the phosphohpases A, B and C that attack other glycerophosphatides, but apparently quite distinct from these enzymes. Kemp et al. (1961) suggested that the enzymes responsible for the degradation of phosphatidyl inositol be referred to as phospho-inositidases. Until these enzymes have been purified further and the possible effects of cationic and anionic amphipathic substances have been fully explored, such a suggestion would appear to be premature. 

The degradation of the glycerophosphatides may be brought about by a variety of enzymes with a wide distribution in nature. The activity of many of these enzymes is altered considerably (1) by the addition of substances, such as ethyl ether, that can penetrate into the lipid micelle and alter the spacing of the molecules oriented at the lipid-water interface and (2) by the presence in the water phase of polyvalent cations or anions that can modify the surface charge in the... 

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