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Plant Physiol, October 1999, Vol. 121, pp. 641-646

Histidine-41 of the Cytochrome b5 Domain of the Borage Delta 6 Fatty Acid Desaturase Is Essential for Enzyme Activity1

Olga Sayanova, Peter R. Shewry, and Johnathan A. Napier*

IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Bristol BS41 9AF, United Kingdom

Unlike most other plant microsomal desaturases, the Delta 6-fatty acid desaturase from borage (Borago officinalis) contains an N-terminal extension that shows homology to the small hemoprotein cytochrome (Cyt) b5. To determine if this domain serves as a functional electron donor for the Delta 6-fatty acid desaturase, mutagenesis and functional analysis by expression in transgenic Arabidopsis was carried out. Although expression of the wild-type borage Delta 6-fatty acid desaturase resulted in the synthesis and accumulation of Delta 6-unsaturated fatty acids, this was not observed in plants transformed with N-terminally deleted forms of the desaturase. Site-directed mutagenesis was used to disrupt one of the axial heme-binding residues (histidine-41) of the Cyt b5 domain; expression of this mutant form of the Delta 6-desaturase in transgenic plants failed to produce Delta 6-unsaturated fatty acids. These data indicate that the Cyt b5 domain of the borage Delta 6-fatty acid desaturase is essential for enzymatic activity.

1 IACR-Long Ashton Research Station receives granted-aided support from the Biotechnology and Biological Sciences Research Council, UK. This work was partially funded by Scotia Pharmaceuticals (Stirling, UK).

* Corresponding author; e-mail jon.napier{at}bbsrc.ac.uk; fax 44-1275-549225.

© 1999 American Society of Plant Physiologists


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