Composition body membrane proteins

The lipid bilayer is not passive in determining membrane protein activity and function, and an accumulating body of evidence indicates that there is a coupling of membrane proteins to lipid bilayer properties. These properties include the effect of bilayer curvature strain (20), the role of specific lipids such as phosphoinositides, (21) and the effect of thickness on membrane protein function (22). The lipid composition, as well as the bilayer properties that result from this composition, act as allosteric regulators of membrane protein function. 

The membrane proteins of maize lipid bodies have been subjected to intensive studies (14). By SDS polyacrylamide gel electrophoresis (Figure 1), the proteins are resolved into several major protein bands, three of low Mr s (19,500, 18,000, and 16,500), and one of higher Mr (40,000). The low Mr proteins have alkaline pi values, and behave as hydrophobic integral proteins, as shown by their resistance to solubilization after repeated washing, amino acid composition, and partitioning in a Triton X-114 system. 

Several aspects of Schwann cell metabolism emerge as potential points of vulnerability to toxicants. The Schwann cell perikaryon (cell body) supports an enormous peripheral structure, the myelin sheath, which, if unwrapped, would dwarf the body of the Schwann cell (see Figure 30.4). Thus, as in the case of axonal transport in neurons, there may be specialized processes involved in supporting the topologically distant myelin. Furthermore, myelin has a specialized lipid and protein composition and a relatively rigid and ordered structure as compared to other membranes. Metabolic perturbations that potentially cause alterations in the composition of lipids and proteins assembled to form this membrane may cause destabilization and collapse of the myelin membrane. In this context, myelin might be much more vulnerable than plasma membranes of other cells. 

Amino Acid Composition. Values vary substantially with differences of species, body location, and technique of isolation, purification, or analysis. However, distinctive patterns are associated with some membrane and fibrous protein isolates (Table 1). High proportions of proline and cystine are consistent with observed chemical and mechanical resistance of membranes (32, 68, 71). Similarly, increased methionine and... 

The detailed chemistry of the stratum corneum is complicated by the membrane s composition, formation, and structure. Some gross chemical characterizations have determined the primary chemical components of the tissue which are shown in Table I (29). The tissue is primarily cellular with approximately 10% extracellular components which are lipid and mucopolysaccharides. The bulk of the tissue is densely packed intracellular fibrous protein associated with lipids, resulting in a dry general body corneum density of 1.35-1.40 gm/cm as determined by a gas displacement technique (30). 

The control of body fluid, sodium, and energy homeostasis is fundamental to mammalian life. The mechanisms involved are complex and rely heavily on receptor-mediated events. Given the ubiquity of n-3 fatty acids in mammalian cell membranes and the reliance of receptor protein activity on membrane lipid composition, we felt it timely to review the mechanisms responsible for body fluid, sodium, and energy homeostasis and to examine evidence suggesting modulation of these processes by n-3 polyunsaturated fatty acids (n-3 PUFAs). 

---