Neutral lipid, definition

The Definition of Lecithin. Lecithin for use in food is defined as A mixture of polar and neutral lipids with a polar lipid content of at least 60%. NB this is different from the scientific usage where lecithin is used as a trivial name for phosphatidylcholine. 

The phospholipases A, (PLAjS) comprise a large group of 1-acyl hydrolases, some of which also degrade neutral lipids (lipases) or remove the acyl group at position 2 in addition to that at position 1 (PLB), and thus must have lysophospholipase activity. Where the enzyme appears to show low selectivity for the sn-l or sn-2 position, the term phospholipase A is used. The term phospholipase B should be restricted to those enzymes where the mechanism involves minimal accumulation of lysophospholipid product. In this section, we consider various enzymes of the PLA type that do not fit a more precise definition in terms of acyl chain selectivity. 

Drugs cross biological membranes most readily in the unionised state. The unionised drug is 1000-10000 times more lipid-soluble than the ionised form and thus is able to penetrate the cell membrane more easily. Chemical compounds in solution are acids, bases or neutral. The Bronsted-Lowry definition of an acid is a species that donates protons (H+ ions) while bases are proton acceptors. Strong acids and bases in solution dissociate almost completely into their conjugate base and H+. Weak acids and weak bases do not completely dissociate in solution, and exist in both ionised and unionised states. Most drugs are either weak acids or weak bases. For an acid, dissociation in solution is represented by ... 

Triton extracts of gastric mucosa contain apparently three materials which can produce channels in lipid bilayers with conductances of 2.5 X 10 ° mho. One material is apparently neutral and cation-selective, another charged, voltage-dependent and anion-selective, whilst the third is non-selective [41]. Material which produces K -selective channels in bilayers has been extracted from excitable tissue [42]. The data obtained so far with these natural channel formers are relatively crude compared with the elegant studies with channel-fdrming antibiotics. Therefore, it is, as yet, unclear whether these materials have definitive roles in biological membrane permeability. 

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