Microsomal elongase system

Figure 21-S. Microsomal elongase system for fatty acid chain elongation. NADH is also used by the reductases, but NADPH is preferred.

This pathway (the microsomal system ) elongates saturated and unsaturated fatty acyl-CoAs (from Cjg upward) by two carbons, using malonyl-CoA as acetyl donor and NADPH as reductant, and is catalyzed by the microsomal fatty acid elongase system of enzymes (Figure 21-5). Elongation of stearyl-CoA in brain increases rapidly during myehnation in order to provide C22 and C24 fatty acids for sphingoEpids. 

Microsomal elongases differ by optimum pH (6.6 for C16 elongase, 7.3 for C18 elongase), temperature, ionic strength and substrate concentrations. Both systems need NADPH as hydrogen donor and malonyl-CoA as C2 donor. Acetyl-CoA is inactive. 

Figure 23-3. Biosynthesis of the co9, co6,and co3 families of polyunsaturated fatty acids. Each step is catalyzed by the microsomal chain elongation or desaturase system 1,elongase 2,A desaturase 3,A desaturase 4,A desaturase. ( .Inhibition.)...

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