Membrane aging Subject

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

PVC-P materials, subjected to ageing under model and climatic conditions, have been extensively tested. Properties are lost as a result of diffusion controlled desorption of the plasticiser and a mathematical description of the ageing process has been formulated to predict lifetime (277). Plasticiser loss on ageing has also been identified in the spectroscopic investigation of roof membranes in service for a varying number of years (240). 

The importance of muscle lysosomal enzymes to the food scientist stems from their apparent involvement in the aging of meats. For example, lysosomal cathepsins are possibly involved in the proteolytic degradation of muscle proteins (31). Lysosomal enzymes exhibit latency that is, they are retained in the lysosomal particle and released only when the particle membrane is damaged. In this regard the lysosomal enzymes are liberated and activated when the particle membranes are weakened by the postmortem drop in pH. Also, lysosomes are very subject to cryoinjury (72), and freezing and thawing of tissues such as muscle releases lysosomal enzymes resulting in autolysis. 

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