Regulation of the biosynthesis of 22 : 5n-6 and 22 : 6n-3: A complex intracellular process

Both 22:4n-6 and 22:5n-3 are synthesized from n-6 and n-3 fatty acid precur sors in the endoplasmic reticulum. The synthesis of both 22:5n-6 and 22:6n- 3 requires that 22:4n-6 and 22:5n-3 are metabolized, respectively, to 24:5n -6 and 24:6n-3 in the endoplasmic reticulum. These two 24-carbon acids must then move to peroxisomes for partial degradation followed by the movement of 22:5n-6 and 22:6n-3 back to the endoplasmic reticulum for use as substra tes in membrane lipid biosynthesis. Clearly an understanding of the control of intracellular fatty acid movement as well as of the reactions carried o ut by microsomes, peroxisomes, and mitochondria are all required in order t o understand not only what regulates the biosynthesis of 22:5n-6 and 22:6n- 3 but also why most tissue lipids selectively accumulate 22:6n-3.