1. BIOC 460 DR. TISCHLER LECTURE 34 SYNTHESIS & PROCESSING OF FATS

2. OBJECTIVES 1.Sequence leading from glucose to fatty acids via lipogenesis including roles of pyruvate carboxylase and pyruvate dehydrogenase. 2.Malic enzyme and acetyl CoA carboxylase 3.For fatty acid synthase: a) substrates/key products; b) sources of NADPH; c) general mechanism 4.Relationship: regulation of carnitine-palmitoyl transferase-I and preventing oxidation of synthesized palmitoyl CoA 5. Eicosanoids: a) fatty acid from which they are derived; b) specific functions of each eicosanoid; c) general pathway of production; effects of glucocorticoids (cortisol) and aspirin

3.  principally in adipose tissue and liver  lipogenesis – cytoplasm; requires acetyl CoA  adipose: FA stored as triacylglycerols via esterification  liver: produces TAG packaged into VLDL and exported  compounds metabolized to acetyl CoA can serve as a fat precursor  glucose = primary source of carbons for fat synthesis. LIPOGENESIS

4. CYTOPLASM MITOCHONDRIAL MATRIX Pyruvate Citrate CS Oxaloacetate PC ATP, CO 2 ADP, P i PPP Pyruvate Glucose Glycolysis FAS Fatty Acids Citrate Acetyl CoA CL ATP, CoA ADP+P i Oxaloacetate ACC ADP, P i CO 2, ATP Malonyl CoA Acetyl CoA NAD, CoA NADH, CO 2 PDH MDH NADH NAD + Malate ME NADP + NADPH CO 2 Figure 1. Export of acetyl CoA as citrate for fatty acid biosynthesis, generation of NADPH and pathway of lipogenesis.

5. KEY MITOCHONDRIAL REACTIONS PYRUVATE CARBOXYLASE pyruvate + CO 2 + ATP  oxaloacetate + ADP + Pi PYRUVATE DEHYDROGENASE pyruvate + NAD + coenzyme A (CoA)  acetyl CoA + CO 2 + NADH

6. Citrate Lyase citrate + CoA + ATP  acetyl CoA + oxaloacetate + ADP + Pi Malate dehydrogenase oxaloacetate + NADH  malate + NAD + Malic Enzyme malate + NADP +  pyruvate + NADPH KEY CYTOPLASMIC REACTIONS INDIRECTLY NEEDED FOR LIPOGENESIS

7. KEY CYTOPLASMIC REACTIONS DIRECTLY NEEDED FOR LIPOGENESIS AND FATTY ACID ACTIVATION Acetyl CoA Carboxylase: acetyl CoA + HCO 3 - + ATP  malonyl CoA + ADP + P i Fatty Acid Synthase: acetyl CoA + 7 malonyl CoA + 14 NADPH + 14 H +  palmitate + 7 CO 2 + 8 CoA + 14 NADP + Acyl CoA Synthetase: (also used for fatty acids other than palmitate) palmitate + ATP + CoA  palmitoyl CoA + AMP + PP i

8. condensation reduction dehydration reduction 2 NADPH 2 NADP + ACPACP CE acp ACPACP CE acp ACPACP CE acp Figure 2. General mechanism for the fatty acid synthase reaction. CE is condensing enzyme. ACP is acyl carrier protein. This row represents the initial steps for priming the reaction with acetyl CoA and the addition of two carbons from malonyl CoA. COO - C=O CH 2 C=O CH 2 C=O CH 3 C=O CH 2 CH 3 malonyl CoA CH 3 C=O acetyl CoA CO 2 CH 3 C=O CH 3 C=O CH 2 CH 3 C=O CH 2 CH 3 C=O CH 2 CH 3 C=O 4-C unit

9. Figure 2. General mechanism for the fatty acid synthase reaction. CE is condensing enzyme. ACP is acyl carrier protein. This row depicts a typical cycle of adding two more carbons to the fatty acid chain. malonyl CoA condensation CO 2 reduction dehydration reduction 2 NADPH 2 NADP + ACPACP CE acp 6-C unit ACPACP CE acp 6-C unit ACPACP CE acp 4-C unit

10. Figure 2. General mechanism for the fatty acid synthase reaction. CE is condensing enzyme. ACP is acyl carrier protein. This row shows the release of the finished product, palmitate, through cleavage by thioesterase. malonyl CoA ACPACP CE acp 16-C unit palmitate ACPACP CE acp 6-C unit 5 more cycles adding 10 more carbons 5CO 2 10NADP + 5malonyl CoA 10NADPH ACPACP CE acp thioesterase cleavage palmitate

11. malic enzyme: Malate + NADP +  Pyruvate + CO 2 + NADPH pentose phosphate pathway: Glucose-6-P + 2 NADP +  Ribulose-5-P + 2 NADPH + CO 2 Sources of NADPH for the Biosynthesis of Fatty Acids.

12. Figure 3. Formation of phosphatidic acid from glycerol-3-P or DHAP, and its conversion to triacylglycerol Lysophosphatidic acid Phosphatidic acid Triacylglycerol NADPH NADP + Diacylglycerol phosphatase CoA Acyldihydroxyacetone phosphate fatty acyl CoA Dihydroxyacetone phosphate fatty acyl CoA CoA ADP ATP glycerol kinase Glycerol-3-P Glycerol CoA fatty acyl CoA CoA fatty acyl CoA Pi

13. EICOSANOIDS hormones localized to tissues where they are produced. prostaglandins, thromboxanes and leukotrienes. derived from arachidonic acid arachidonic acid from linoleic acid an essential fatty acid Table 1. Physiological functions of eicosanoids. EicosanoidFunctions prostaglandinsinflammation, fever production, prevent platelet aggregation (prevent clotting); induce labor thromboxanesproduced by platelets to promote their aggregation (blood clotting) leukotrienesallergic reactions

14. Membrane Phospholipid Phospholipase A 2 Arachidonic acid Lipoxygenase Leuokotrienes Cyclooxygenase PGH 2 Thromboxanes in platelets Prostaglandins in many cells Figure 4. Conversion of arachidonic acid to eicosanoids. inhibited by glucocorticoids inhibited by aspirin, ibuprofen