{'fraction_non_alphanumeric': 0.04120111731843575, 'fraction_numerical': 0.006983240223463687, 'mean_word_length': 5.176724137931035, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Calmodulin-stimulated calcium pumping ATPases located at higher plant intracellular membranes: a significant divergence from other eukaryotes?

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.