Desaturation - length of 16-18 carbons is required The...

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Desaturation Desaturation of fatty acids can also occur in most tissues. Desaturation: The Overall Reaction RCH 2 CH 2 ...CH 2 COSCoA + NADPH + H + + O 2 --> RCH=CH...CH 2 COSCoA + NADP + + 2H 2 O A cis double bond is formed. The reaction requires an electron transport system involving: 1. cytochrome b 5 2. desaturase 3. NADPH-cytochrome b 5 reductase This complex system avoids generating H 2 O 2 in the vicinity of the sensitive double bonds. The system is associated with the membranes of the endoplasmic reticulum. Desaturation: Specificity In humans there are four distinct desaturases, each with a different specificity: 9 , 6 , 5 , 4 (that is, they act at the 9-, 6-, 5- or 4-carbons.) A minimum chain
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Unformatted text preview: length of 16-18 carbons is required. The specificity of distance from the carboxyl carbon, along with the need for a 16-18 carbon chain means that n-6 and n-3 fatty acids are not synthesized in humans. Because some of these fatty acids are metabolically essential, they must be supplied in the diet. Desaturation and 2-carbon elongation often alternate, e.g. , conversion of dietary linoleic acid (18:2 9,12 ) to arachidonic acid (20:4 5,8,11,14 ), which is important because it is a precursor of eicosanoids. 18:2 9,12--> 18:3 6,9,12--> 20:3 8,11,14--> 20:4 5,8,11,14-Mobilization and Transport of Adipose Fatty Acid...
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