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A manganese-dependent protein kinase in gastric gland cytosol
Abstract:
A protein kinase activity completely dependent on Mn2+ was studied in the cytosolic fraction from rabbit-isolated gastric glands. The manganese-dependent protein kinase (MNPK) activity phosphorylated major 33 kd (pp33) and minor 140 kd (pp140) endogenous proteins. The MNPK activity displayed a Kact for Mn2+ of 7.5 mmol/L. MNPK showed no preference for adenosine triphosphate or guanosine triphosphate with a Kact of 10 mumol/L for both. The kinase was differentiated from other known kinases since calmodulin, cyclic adenosine monophosphate, and phospholipids failed to stimulate pp33 phosphorylation. Furthermore, the protein kinase inhibitors trifluoperazine, the Walsh inhibitor protein, and heparin, as well as the phosphatase inhibitor p-nitrophenylphosphate failed to alter MNPK activity. The results indicate that novel MNPK activity is present in gastric gland cytosol. Elucidation of intracellular protein kinase activities may provide insights into the regulation of gastric secretory process.
Insights
Researchers discovered a novel manganese-dependent protein kinase (MNPK) in rabbit gastric glands. This MNPK phosphorylates specific endogenous proteins, offering potential insights into gastric secretion regulation.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Gastric glands are crucial for digestion and nutrient absorption.
- Intracellular protein kinases play vital roles in cellular signaling pathways.
- Understanding novel kinase activities can elucidate complex physiological processes.
Purpose of the Study:
- To characterize a novel protein kinase activity dependent on manganese (Mn2+) in rabbit gastric gland cytosol.
- To identify the substrates and regulatory properties of this manganese-dependent protein kinase (MNPK).
- To differentiate MNPK from known kinase families and assess its potential role in gastric function.
Main Methods:
- Fractionation of rabbit gastric glands to isolate cytosolic components.
- Assay of protein kinase activity using endogenous substrates.
- Determination of kinetic parameters (Kact) for Mn2+ and nucleotide triphosphates.
- Differential screening using known kinase modulators (calmodulin, cAMP, phospholipids, inhibitors).
Main Results:
- A novel manganese-dependent protein kinase (MNPK) activity was identified in gastric gland cytosol.
- MNPK phosphorylated major 33 kDa (pp33) and minor 140 kDa (pp140) endogenous proteins.
- MNPK exhibited a Kact for Mn2+ of 7.5 mmol/L and showed no nucleotide preference (Kact 10 μmol/L for ATP/GTP).
- MNPK activity was not modulated by calmodulin, cAMP, phospholipids, or tested inhibitors, distinguishing it from known kinases.
Conclusions:
- A novel MNPK activity exists in gastric gland cytosol, distinct from previously characterized kinases.
- This MNPK phosphorylates specific endogenous proteins, suggesting a unique regulatory role.
- Further investigation of MNPK may reveal its involvement in the regulation of the gastric secretory process.