Desaturation of palmitate and stearate by cell-free fractions from soybean cotyledons

Homogenates of cotyledons from immature soybean seeds were fractionated by centrifugation. Cell-free preparations actively desaturated 1-¹⁴C-palmitate and 1-¹⁴C-stearate to produce 9,10-unsaturated acids. The 9-desaturase activity was present mainly in supernatant fractions (22,000 and 105,000 xg). These fractions also desaturated oleate to linoleate and elongated C₁₄, C₁₆ and C₁₈ acids. In view of this versatility of desaturase systems in the soybean, including the 9-desaturase(s) for C₁₄, C₁₆ and C₁₈ saturated acids, there would not seem to be further need to consider a separate plant pathway for biosynthesis of unsaturated fatty acids. Published as Journal Paper No. 3197, AES, Purdue University, Lafayette, Indiana 47907.