Firmly-Bound Lipids

Anderson found that a substance of lipid nature was associated with the skeletal material of acid-fast bacilli. This lipid was not removed by neutral organic solvents but could be extracted with an ethereal or chloroform solution of hydrogen chloride. Saponification of these firmly-bound lipids yielded a polysaccharide having properties similar to those of the polysaccharide obtained from the purified wax. Phthiocerol was not detected. The polysaccharide was shown to contain 

D-arabinose, D-mannose and D-galactose. immune serum in high dilution. 

Comparison of Properties of Polysaccharides Isolated from Firmly-bound Lipids of Human and Avian Strains of M. Tuberculosis and Leprosy Bacilli (After Anderson ) 

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Phospholipids were first identified by Hammerschlag and Kresling. Long and Campbell concluded that the waxy substance present in M. tuberculosis was a difficultly hydrolyzable ester of an alcohol of high molecular weight. A systematic and thorough examination of the lipids of the bacilli has been undertaken by Anderson and coworkers. He was able to differentiate between four main lipid fractions (1) phosphatides (2) acetone-soluble fats (3) waxes (4) firmly bound lipids. 

However, Rudie et al. (1981) reported the presence of firmly bound EPR-silent copper in their luciferase preparation that was 40 times more active than that obtained by Bellisario et al. (1972). Thus, copper may be a functional part of luciferase. According to Rudie et al. (1981), the luciferase contains carbohydrate (6%), lipid (2%), copper (up to 4g-atom per mole), and an unusually high content of proline plus hydroxyproline (11% by weight). 

At each step in the food web, organochlorine contaminants undergo biomagnification and remain firmly bound to lipid molecules. The term biomagnification is self-explanatory, whereby the minuscule levels of toxic chemicals in the water become concentrated in wildlife bodies, often ending up at high concentrations in organisms at the top of the food web.6-8... 

Preliminary experiments suggested that appreciable amounts of zinc in leukocytes are firmly bound to proteins, since only a very small fraction of the metal was found dialyzable. White cells from human subjects were frozen, thawed, diluted with distilled water, and then extracted with ether to remove lipids. The total white cells contained 13,000 uS-, the materials extracted by ether contained 39 /xg. of zinc, or 0.13% of the total zinc present. Investigations, therefore, centered on the zinc presumably bound to lipid-free protein. 

Endotoxins are produced primarily by gramnegative bacteria. They act as antigens, are firmly bound to the bacterial cell wall and are complex in nature. They have protein, poly-saccharide and lipid components. Endotoxins are relatively heat stable and are in general active without a latent period. The toxins causing typhoid and paratyphoid fevers, salmonellosis and bacterial dysentery are in this group. Salmonellosis is very serious. It is an infection by toxins of about 300 different but closely related organisms. The infec-... 

Figure 41-7. The fluid mosaic model of membrane structure. The membrane consists of a bimolecu-lar lipid layer with proteins inserted in it or bound to either surface. Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, while others are embedded in either the outer or inner leaflet of the lipid bilayer. Loosely bound to the outer or inner surface of the membrane are the peripheral proteins. Many of the proteins and lipids have externally exposed oligosaccharide chains. (Reproduced, with permission, from Junqueira LC, Carneiro J Basic Histology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

The long chain acyl-CoA synthetases are firmly membrane bound and can only be solubilized by the use of detergents. Within the cell, activity has been detected in endoplasmic reticulum and the outer mitochondrial membrane with small amounts in peroxisomes (when the latter are present). There is some dispute as to whether the activity present in mitochondrial and microsomal fractions is due to the same enzyme. Because long chain fatty acid activation is needed for both catabolism ( -oxidation) and for synthesis (acylation of complex lipids) it would be logical if the long chain acyl-CoA synthetases of mitochondria and the endoplasmic reticulum formed different pools of cellular acyl-CoA. This compartmentation has been demonstrated with yeast mutants where it plays a regulatory role in lipid metabolism (section 3.2.7) and, perhaps, in other organisms. 

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