Characterization of a structurally and functionally diverged acyl- acyl carrier protein desaturase from milkweed seed.
A cDNA for a structurally variant acyl- acyl carrier protein ( ACP) desaturase was isolated from milkweed (Asclepias syriaca) seed, a tissue enriched in palmitoleic (16:1delta9)* and cis-vaccenic (18:1delta11) acids. Extracts of Escherichia coli that express the milkweed cDNA catalyzed delta9 desaturation of acyl- ACP substrates, and the recombinant enzyme exhibited seven- to ten-fold greater specificity for palmitoyl (16:0)-ACP and 30-fold greater specificity for myristoyl (14:0)-ACP than did known delta9-stearoyl (18:0)-ACP desaturases. Like other variant acyl- ACP desaturases reported to date, the milkweed enzyme contains fewer amino acids near its N-terminus compared to previously characterized delta9-18:0- ACP desaturases. Based on the activity of an N-terminal deletion mutant of a delta9-18:0- ACP desaturase, this structural feature likely does not account for differences in substrate specificities.[1]References
- Characterization of a structurally and functionally diverged acyl-acyl carrier protein desaturase from milkweed seed. Cahoon, E.B., Coughlan, S.J., Shanklin, J. Plant Mol. Biol. (1997) [Pubmed]
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