Enzymes of TAG Synthesis

Accumulating evidence for important functions of enzymes involved in lipid synthesis and its control has been obtained through targeted disruption in rodent models of the corresponding genes (Fig. 11.2). However, direct links between abnormal expression or genetic variants and human disorders, such as obesity, hyperlipidemia, insulin resistance, and NIDDM await further clarification. Glycerol- 

The final step in TAG synthesis occurs by the action of acyl-GoA diacylglycerol acyltransferase (DGAT) witli DAG and fatty acyl-GoA as substrates (Fig. 11.2). DGAT is assumed to be a microsomal enzyme. The membrane-bound enzyme has been only partially purified from rat liver microsomes [124]. Gases and coworkers [125] have identified a mouse cDNA encoding DGAT and, in addition, an expressed sequence tag clone that shared regions of similarity with acyl-GoA cholesterol acyltransferase, an enzyme that also uses fatty acyl-CoA as a sub- 

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The activity of the E.R. marker enzyme, CDP-choline DAG transferase for the top 15 fractions of a gradient is shown in figure 3. CDP-choline DAG transferase activity like LPC-AT (figure 2) copurifies with the enzymes of TAG synthesis in the dense fraction (9-13),but is almost undetectable in the light vesicle fraction (3-5). Marker enzymes for the plastids, cytosol, mitochondria and chlorophyll were also assayed (data not shown), however these organelles were found not to be associated with TAG synthesis. 

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