mehta50 - Eicosanoid Metabolism Medical Biochemistry...

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Eicosanoid Metabolism Medical Biochemistry Lecture #50
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METABOLISM OF UNSATURATED  FATTY ACIDS AND EICOSANOIDS   • Animals  have  limited  ability  in  desaturating  fatty acids.   • Dietary intake of certain polyunsaturated fatty  acids  derived  from  a  plant  source  is  necessary.  • These  essential  fatty  acids  give  rise  to  eicosanoic  (C20)  fatty acids, from  which  are  derived  families  of  compounds  known  as  eicosanoids.  • Eicosanoids  include  prostaglandins,  thromboxanes, leukotrienes, and lipoxins. 
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Some polyunsaturated fatty acids  are essential : • Double bonds are present in  cis -configuration.  • Palmitoleic and oleic acids are not essential in the  diet, because the tissues are capable of introducing  a  double  bonds  at  the  9 position  into  the  corresponding fatty acids. • In most mammals, double bonds can be introduced  at  the 4, 5, 6, and 9 positions  but  never  beyond the  9 position. • Linoleic  and  α -linolenic  acids  are  known  as  nutritionally  essential  fatty  acids.    Arachidonic  acid  can  be  formed  from  linolenic  acid  in  most  mammals.
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Monounsaturated fatty acids are  synthesized by a  9 desaturase system:   • Several  tissues  including  the  liver  is  responsible  for formation of monounsaturated fatty acids from  saturated fatty acids.  9  desaturase  system  in  the  endoplasmic  reticulum  will  catalyze  conversion  of  palmitoyl- CoA  or  stearoyl-CoA  to  palmitoleoyl-CoA  or  oleoyl-CoA, respectively.  • The  enzyme  appear  to  be  similar  to  cytochrome  b5,  and  consists  of  three  component  proteins,  NADH-cytochrome b5 reductase, cytochrome b5,  and  a  cynamide-sensitive  desaturase  containing  non-heme iron.  
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Synthesis of polyunsaturated  fatty acids involves desaturase  and elongase enzyme systems   • In higher animals, additional double bonds 
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mehta50 - Eicosanoid Metabolism Medical Biochemistry...

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