Catalyzes the first and rate-limiting reaction of the four reactions that constitute the long-chain fatty acids elongation cycle. This endoplasmic reticulum-bound enzymatic process allows the addition of 2 carbons to the chain of long- and very long-chain fatty acids (VLCFAs) per cycle. Condensing enzyme that catalyzes the synthesis of polyunsaturated very long chain fatty acid (C20- and C22-PUFA), acting specifically toward polyunsaturated acyl-CoA with the higher activity toward C20:4(n-6) acyl-CoA. May participate in the production of polyunsaturated VLCFAs of different chain lengths that are involved in multiple biological processes as precursors of membrane lipids and lipid mediators. Essential for the formation of C24:5(n-6) up to C30:5(n-6) PUFAs in testis, these fatty acids being indispensable for normal spermatogenesis and fertility. a very-long-chain acyl-CoA + H(+) + malonyl-CoA = a very-long-chain 3-oxoacyl-CoA + CO2 + CoA (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + H(+) + malonyl-CoA = (7Z,10Z,13Z,16Z)-3-oxodocosatetraenoyl-CoA + CO2 + CoA (7Z,10Z,13Z,16Z)-docosatetraenoyl-CoA + H(+) + malonyl-CoA = (9Z,12Z,15Z,18Z)-3-oxotetracosatetraenoyl-CoA + CO2 + CoA (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA + H(+) + malonyl-CoA = (7Z,10Z,13Z,16Z,19Z)-3-oxodocosapentaenoyl-CoA + CO2 + CoA (7Z,10Z,13Z,16Z,19Z)-docosapentaenoyl-CoA + H(+) + malonyl-CoA = (9Z,12Z,15Z,18Z,21Z)-3-oxotetracosapentaenoyl-CoA + CO2 + CoA Lipid metabolism; polyunsaturated fatty acid biosynthesis. Highly expressed in testis, lower level in liver. Weakly expressed in white adipose tissue, brain and kidney. The C-terminal di-lysine motif may confer endoplasmic reticulum localization. Belongs to the ELO family. ELOVL2 subfamily.