%0 Journal Article
%T Identification of a soluble phosphatidate phosphohydrolase in the developing cotyledons of <i>Momordica</i> <i>charantia</i>
%A Abul H. J. Ullah
%A Kandan Sethumadhavan
%J Advances in Biological Chemistry
%P 11-17
%@ 2162-2191
%D 2013
%I Scientific Research Publishing
%R 10.4236/abc.2013.31002
%X <p style=\"text-align:justify;\">
	<span style=\"font-size:10.0pt;\"><span style=\"font-size:12px;\">Phosphatidate phosphatase (EC 3.1.3.4), PAP, catalyzes
the dephosphorylation of phosphatidate (PtdOH) to form diacylglycerol. In
eukaryotes, PAP driven reaction is the committed step in the synthesis of triacylglycerol.
A Mg</span><sup><span style=\"font-size:12px;\">2+</span></sup><span style=\"font-size:12px;\"> independent PAP activity was identified in the soluble
extract of </span><i><span style=\"font-size:12px;\">Momordica charantia</span></i><span style=\"font-size:12px;\"> cotyledons undergoing maturation. While the microsomal fraction of the
extract gave only 10% of the PAP activity, the remaining 90% of the activity
was associated with the soluble fraction. At pH 3.0, the soluble PAP was bound
to S column and eluted with glycine-HCl buffer containing high salt. The pH and
temperature optima of the PAP activity were 6.0 and 53</span></span><span style=\"font-family:ËÎÌå;\">¡æ</span>, respectively. Under
optimum assay condition, the V<sub>max</sub> and K<sub>m</sub> for dioleoyl
phosphatidic acid were 1.89 ¦Çkat/mg of protein and 142 ¦ÌM, respectively. For
the synthetic substrate, <i style=\"font-size:10pt;\"><span style=\"font-size:12px;\">¦Ñ</span></i>-nitrophenylphosphate, <i style=\"font-size:10pt;\"><span style=\"font-size:12px;\">¦Ñ</span></i>- NPP, the V<sub>max</sub> and K<sub>m</sub> were 10.4 ¦Çkat/mg of protein and 107 ¦ÌM, respectively. The inclusion of Mg<sup>2+</sup> and <i style=\"font-size:10pt;\"><span style=\"font-size:12px;\">¦Â</span></i>-mercaptoethanol into the
reaction mix did not change the enzyme activity nor did the addition of
N-ethylmaleimide and phenylglyoxal, which indicates that cysteine and arginine
are not involved in catalysis of PtdOH. The addition of Mg<sup>2+</sup> up to
10 mM also did not change the level of PAP activity. Triton X-100, however,
inhibited the activity. This is the first documented case of an <i style=\"font-size:10pt;\"><span style=\"font-size:12px;\">in vitro</span></i> PAP activity in the developing
cotyledons of <i style=\"font-size:10pt;\"><span style=\"font-size:12px;\">Momordica charantia</span></i>. The
PAP described here could serve as a model for lipin-1 or lipin-2 in humans. Mutations
in these genes lead to acute myoglobinuria in human infants.
</p>
%K PAP
%K EC 3.1.3.4
%K Phosphatidic Acid Phosphatase
%K Momordica Charantia
%U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=27784