Glycerolphosphate

Mitochondria have an outer membrane that is permeable to most metabohtes, an inner membrane that is selectively permeable, and a matrix within (Figure 12-1). The outer membrane is characterized by the presence of various enzymes, including acyl-CoA synthetase and glycerolphosphate acyltransferase. Adenylyl kinase and creatine kinase are found in the intermembrane space. The phospholipid cardiolipin is concentrated in the inner membrane together with the enzymes of the respiratory chain. 

The acoustic micrograph in Fig. 1.5(a) came from a 5-week-old preparation. It was fixed in alcohol, and stained for alkaline phosphatase and, with von Kossa stain, for biomineral material. The biomineral material of interest here is hydroxyapatite, the principal crystalline mineral constituent of bone. The ordered structure visible within the matrix is not seen with either the light or electron microscopes. But the acoustic microscope can also work perfectly well with unfixed, unstained specimens. Figure 1.5(b) is an acoustic micrograph of matrix and cells from a 17-year-old male. In addition to the standard ingredients of culture medium, these cells were specifically stimulated with beta-glycerolphosphate and a vitamin C preparation. Because the acoustic... 

Figure 10-5. Intrahepatic metabolism of free fatty acids (FFA). CPT I, CPT II, carnitine palmitoyltransferase I, II, respectively LCFA, long-chain fatty acid VLDL, very low-density lipoprotein. 1, Long-chain acyl-CoA synthase 2, acetoacetyl-CoA thiolase 3, hydrox-ymethylglutaryl-CoA synthase 4, hydroxymethylglutaryl-CoA lyase 5, 3-hydroxybutyrate dehydrogenase 6, acetyl-CoA carboxylase 7, fatty acid synthase 8, glycerolphosphate acyltransferase Reprinted with permission from Girard et al. (1992).

Fig. 8.16 Biosynthesis of L-Trp. Compounds ANT, anthrani-late CDRP, l-(o-carboxyphenylamino)-l-deoxyribulose-5-phosphate I3GP, indole-3-glycerolphosphate IND, indole PRAA, phosphoribosyl anthranilate PRPP, 5-phosphoribosyl-a-pyrophosphate.

Alpha-glycerolphosphate 7 Cytosol/Mitochondria Shuttle for reducing equivalents... 

If we assume completion of the reaction when been converted to P (a-glycerolphosphate), then... 

Glucose metabolism in glycosomes of trypanosomes (a) Glycerolphosphate kinase (b) Glycerol kinase. 

The conversion of giycerol-3-phosphate (G-3-P) into dihydroxyacetone phosphate (DHAP) in glycosomes generates reducing equivalents, which enter the mitochondria and convert molecular oxygen into water. This respiratory reaction takes place in the presence of the glycerol-3-phosphate oxidase (glycerolphosphate oxidase, GPO) system. It is a complex enzyme system, which is unique to salivarian trypanosomes this is not found in mammalian cells [7]. Further, GPO is cytochrome free and is bound to the inner membrane of mitochondria (Chart 2). 

Malate and a-glycerolphosphate shuttles. The shuttling of reducing power from cytosolic NADH into the mitochondrion. The malate shuttle (top portion) is more complex, but yields more highenergy phosphates. Malate can move reducing power into or out of the mitochondria. The a-glycerolphosphate shuttle only moves reducing power from the cytosol to the mitochondria. 

Triglyceride and phospholipid formation. This figure depicts the formation of triacylglycerol from a-glycerolphosphate and fatty-acyl CoA. The formation of phosphatidylethanolamine and phosphatidylcholine from scratch (i.e., from serine and methionine methyl groups) is also shown. The formation of phosphatidylcholine, starting with choline, is also depicted and is the major pathway for phosphatidylcholine synthesis. 

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