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. 2002 Sep;130(1):22–46. doi: 10.1104/pp.004770

Figure 1.

Figure 1

PI metabolism. The different steps in the synthesis of PIs and the lipid kinases catalyzing the different reactions are indicated. PtdIns(3,4,5)P3 is present in animal cells but has not been detected in plant tissues, so far. In animal cells, PtdIns(3,4)P2 can be generated from PtdIns4P by a PtdIns 3-kinase or by an as-yet-unidentified PIPkin from PtdIns3P. Plant cells do not contain any homolog of the heterodimeric inositol lipid 3-kinases that are able to phosphorylate PtdIns4P to PtdIns(3,4)P2 and PtdIns(4,5)P2 to PtdIns(3,4,5)P3. PtdIns(4,5)P2 can be synthesized by type I and type II PIPkins from PtdIns4P and PtdIns5P, respectively. On the basis of sequence comparison, plants cells do not possess type II PIPkins. PtdIns5P is present in plants, but an enzyme capable of producing it has not been identified.