Abstract:Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6 -7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1␤ converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.

Cell-free homogenates of spinach leaves incorporated glycerophosphate-32P into phosphatides when supplied with adenosine triphosphate, Mg++and coenzyme A (CoA). Most of the activity of the homogenate was associated with the microsome fraction sedimented at 104,000 × g, but some activity was also present in the chloroplast fraction. In all systems, most of the32P incorporated appeared in phosphatide acid (+ lysophosphatidic acid), with small to trace amounts in phosphatidyl glycerol and phosphatidyl inositol. Coenzyme A and adenosine triphosphate + Mg++were obligatory cofactors for the incorporation of α-glycerophosphate-32P but acetate + bicarbonate, cytidine triphosphate, or light were not essential. The results demonstrate the presence of acyl-CoA:L-glycerol-3-phosphate O-acyltransferase in the microsome fraction of spinach leaves and also indicate the existence of enzyme systems catalyzing the conversion of phosphatidic acid to phosphatidyl inositol and phosphatidyl glycerol.

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The kinetics of incorporation of 32P from orthophosphate-32P or DL-α-glycerophosphate-32P into the phosphatides of Chlorella vulgaris during photosynthesis was studied. Rapid labelling of phosphatidyl glycerol was observed with both precursors, followed by lower rates of incorporation into lecithin, phosphatidyl ethanolamine, and phosphatidyl inositol. The results are discussed in the light of biosynthetic pathways known for animal and bacterial cells.

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