A-Glycerol phosphate

Furthermore, if the antibiotic passes membranes through a specific port of entry, its mutational loss leads to resistance. The lack of the outer membrane protein OprD in P. aeruginosa causes resistance to the (3-lactam antibiotic imipenem. Fosfomycin passes the cytoplasmic membrane via an L-a-glycerol phosphate permease. This transport system is not essential for bacterial growth and therefore mutants with a reduced expression are frequently selected under therapy. 

Electrons from NADH outside the mitochondria are transported into the mitochondria by the malate-aspartate shuttle or the a-glycerol phosphate shuttle. 

The other shuttle is the malate-aspartate shuttle. The advantage of this shuttle is that it gives you 3 ATPs for the oxidation of each cytoplasmic NADH. In red muscle, heart, and brain tissues the malate-aspartate shuttle is the major pathway for shuttling electrons into mitochondria. In white muscle, the a-glycerol phosphate shuttle predominates (Fig. 14-2). 

Rotenone inhibits the transfer of electrons from NADH into the electron transport chain. The oxidation of substrates that generate NADH is, therefore, blocked. However, substrates that are oxidized to generate FADH2 (such as succinate or a-glycerol phosphate) can still be oxidized and still generate ATP. Because NADH oxidation is blocked, the NADH pool becomes more reduced in the presence of rotenone since there s nowhere to transfer the electrons. 

Many enzymes in the mitochondria, including those of the citric acid cycle and pyruvate dehydrogenase, produce NADH, aU of which can be oxidized in the electron transport chain and in the process, capture energy for ATP synthesis by oxidative phosphorylation. If NADH is produced in the cytoplasm, either the malate shuttle or the a-glycerol phosphate shuttle can transfer the electrons into the mitochondria for delivery to the ETC. Once NADH has been oxidized, the NAD can again be used by enzymes that require it. 

FADH is produced by succinate dehydrogenase in the citric acid cycle and by the a-glycerol phosphate shuttle. Both enzymes are located in the inner membrane and can reoxidize FADHj directly by transferring electrons into the ETC. Once FADH2 has been oxidized, the FAD can be made available once again for use by the enzyme. 

All these components are in the inner membrane of the mitochondria as shown in Figure I-I3-3. Succinate dehydrogenase and the a-glycerol phosphate shuttle enzymes reoxidize their FADHj and pass electrons directly to CoQ. 

A glycerol phosphate polymer containing 1,3-linkages could be hydrolyzed in alkali by fission at either side of each phosphodiester linkage, to give glycerol and its mono- and di-phosphates in proportions which would... 

Fio. 6. Formation and Structural Determination of an Alkali-stable Phosphodiester in the Hydrolysis of a Glycerol Phosphate Polymer. 

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