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Alkaline phosphatase and protein kinase(s) activities in free cytoplasmic mRNPs from human term placenta
Abstract:
Free mRNPs isolated from human term placental tissue were examined for protein kinase and phosphoprotein-phosphatase activities. Free mRNPs incubated with [gamma-32P]ATP in a protein kinase standard buffer show self-phosphorylation in the absence of exogenous substrates. Treatment of phosphorylated products with alkali showed a significant phosphorylation of tyrosine residues within the mRNP-proteins. An alkaline-phosphatase activity was found to be tightly associated with the mRNPs. Both heat stable and heat labile alkaline phosphatase activities were found in the mRNPs. Heat labile alkaline phosphatase is the major isoenzyme form of the mRNPs. The existence of both protein kinase(s) and alkaline phosphatase activities in placental free cytoplasmic mRNPs might suggest that a balance between phosphorylation, specifically on tyrosine residues, and dephosphorylation states of some of the mRNP-proteins is relevant for their physiological functions, and may therefore play a role in the regulation of mRNPs' metabolism and, consequently, in mRNA translation.
Insights
Human placental messenger ribonucleoprotein particles (mRNPs) possess both protein kinase and alkaline phosphatase activities. This balance of phosphorylation and dephosphorylation may regulate mRNP metabolism and mRNA translation.
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- Messenger ribonucleoprotein particles (mRNPs) are crucial for mRNA transport and translation.
- The enzymatic activities associated with mRNPs, particularly phosphorylation and dephosphorylation, are not fully understood.
- Investigating these activities in placental tissue provides insights into maternal-fetal communication and development.
Purpose of the Study:
- To investigate the presence and nature of protein kinase and phosphoprotein-phosphatase activities in free cytoplasmic mRNPs from human term placental tissue.
- To determine if these activities are intrinsic to the mRNPs and their potential role in regulating mRNP function.
Main Methods:
- Isolation of free mRNPs from human term placental tissue.
- Assay of protein kinase activity using [gamma-32P]ATP, including analysis of phosphorylation sites (e.g., tyrosine).
- Assay of alkaline phosphatase activity, including characterization of heat-stable and heat-labile forms.
Main Results:
- Isolated mRNPs exhibited self-phosphorylation activity, with significant phosphorylation occurring on tyrosine residues.
- Alkaline phosphatase activity was tightly associated with mRNPs, with both heat-stable and heat-labile isoenzymes detected.
- The heat-labile alkaline phosphatase was identified as the major isoenzyme form present in placental mRNPs.
Conclusions:
- The co-existence of protein kinase and alkaline phosphatase activities within placental free cytoplasmic mRNPs suggests a regulatory mechanism.
- A balance between tyrosine phosphorylation and dephosphorylation of mRNP proteins is likely important for their physiological functions.
- These enzymatic activities may play a critical role in regulating mRNP metabolism and, consequently, mRNA translation during placental development.