H. Honda et al., An isozyme of the NADP-malic enzyme of a CAM plant, Aloe arborescens, withvariation on conservative amino acid residues, GENE, 243(1-2), 2000, pp. 85-92
In Aloe arborescens, an obligate CAM plant, Western analysis detected three
major isoforms of NADP-malic enzyme (NADP-ME), 72 kDa with a pI of 6.0, 65
kDa with a pi of 5.6 and 65 kDa with a pI of 5.5. Among them, the 65 kDa p
rotein with a pI of 5.5 was leaf-specific, and the 65 kDa protein with a pI
of 5.6 was found only in roots, whereas the 72 kDa protein was uniformly d
etected in both organs. Activity staining indicated enzyme activity of both
65 kDa NADP-MEs but little activity of the 72 kDa protein. A cDNA clone en
coding a leaf-abundant NADP-ME, AME1, was isolated. Deduced amino acid sequ
ence of AME1 showed a high degree of homology to known NADP-MEs, but it was
also found that AME1 contained substitutions on five conservative amino ac
id residues, some of which have been predicted to be important for their en
zyme activity. Transgenic rice carrying the aloe AME1 gene efficiently prod
uced an additional 65 kDa protein with a pI of 5.5 as an active NADP-ME. Th
ese results indicate that AME1 corresponds to the leaf-specific 65 kDa NADP
-ME, which may be involved in CAM photosynthesis. It was also shown that su
bstitutions of these conservative amino acid residues identified in AME1 st
ill allowed it to give enzyme activity. (C) 2000 Elsevier Science B.V. All
rights reserved.