Calmodulin‐stimulated calcium pumping ATPases located at higher plant intracellular membranes: a significant divergence from other eukaryotes?
1994
Evans, David E.
The plasma membrane (PM) of all eukaryotes so far investigated contains a P‐type Ca2+‐pumping ATPase responsible for maintaining low cytosolic free calcium concentrations. In animal cells this has been shown to be a type of Ca2+‐pump which is directly stimulated by binding the calcium‐dependent regulator protein calmodulin. These PM Ca2+‐pumps have been named ‘PM‐type’ as they appear to be exclusively located at the PM and not in intracellular membrane (IM) fractions. Recent progress on higher plant cells reveals that they possess calmodulin‐stimulated Ca2+‐pumps of the ‘PM‐type’. However, these calmodulin‐stimulated Ca2+‐pumps appear to be located not only at the PM but also in intracellular membranes, probably the endoplasmic reticulum (ER). The evidence is also convincing that these IM‐located Ca2+‐pumps are directly stimulated by calmodulin (possess a calmodulin‐binding region) and are true ‘PM‐type’ Ca2+‐pumps. This appears to represent a marked divergence between plant and animal cell Ca2+‐pumps. Recently, molecular cloning has revealed that plant cells also contain a Ca2+‐pump which is not directly stimulated by calmodulin and which strongly resembles the mammalian ER/SR type of Ca2+‐pump. The significance of these findings for plant cell function is discussed.
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