The biosynthesis of unsaturated fatty acids by bacilli. 3. Uptake and utilization of exogenous palmitate.

The apparent in viva substrate specificities for six bacilli desaturases, previously shown to insert a c&double bond into position five of palmitate and of one which desaturates in position 10 were determined in whole cells by a variety of methods. In addition, the positional specificity of double bond insertion and the rate of temperature-mediated inactivation of these desaturases were also determined. The results can be summarized as follows. In five bacilli strains only one desaturase (A”) was found while in one organism (Bacillus licheniformis 9259), both A5 and Alo desaturation were observed and it was shown that at least two different desaturases were involved. For all desaturases, with the possible exception of the A5desaturase of B. licheniformis 9259, maximal desaturation activity was found with pahnitate (n-ClsZo) with activity for the n-saturated substrates decreasing in the order Cl6 > Cl7 > C18. The A’O-desaturase of B. licheniformis 9259 showed almost absolute specificity for palmitate while the A5-desaturases of the other species showed quantitative variations in their preferences for these three substrates ranging from that of Bacillus megaferium 14581, whose relative desaturation activity was 1.00, 0.57, and 0.16 toward ~-CN:O, n-C17:0, and R-&,:~, respectively, to that of Bacillus pumilis 7061 (1.00, 0.81, and 0.74 for the same three fatty acids). Pentadecanoic acid (n-C1,:,), tested only in the latter two organisms, had a specificity relative to pahnitate of about 0.5 in both cases. The As-desaturase of B. licheniformis 9259 favored n-ClT:o over n-Cls.o but, because of competition with the A’O-desaturase, its relative activity toward n-Cx:o could not be determined. In the three organisms tested (B. megaferium 14581, B. pumilis 7061, and B. Zicheniformis 9259) branched chain fatty acids and A9 or Alo mono-unsaturated fatty acids were also desaturated. 14-Methylpentadecanoate (iso-C&:0) was almost as good a substrate