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DARPP-32 (dopamine and cAMP-regulated phosphoprotein, M(r) 32,000) is a membrane protein in the bovine parathyroid
L M Matovcik1, H C Hemmings, B K Kinder
1Department of Surgery, West Haven Department of Veterans Affairs Medical Center, CT 06516, USA.
Abstract:
A distinct form of DARPP-32, a protein phosphatase-1 inhibitor, has been identified in bovine calf parathyroid glands. Immunoblot analysis of parathyroid tissue revealed a 32 kDa protein present predominantly in a particulate fraction; it remained particulate after treatment with 1.0 M NaCl or 0.1 M Na2CO3. Metabolic labeling of parathyroid cells with mevalonolactone demonstrated that DARPP-32 is isoprenylated. Immunocytochemical localization studies demonstrated that DARPP-32 is present in vesicles throughout the cytoplasm of parathyroid cells, and that protein phosphatase-1 gamma is concentrated in the region of the plasma membrane. Thus, in contrast to the predominately soluble form of DARPP-32 that has been characterized in selected areas of the central nervous system, the parathyroid form is tightly associated with intracellular membranes.
Insights
A novel form of DARPP-32, a protein phosphatase-1 inhibitor, was found in bovine parathyroid glands. This distinct DARPP-32 variant is associated with intracellular membranes, unlike its soluble counterpart in the central nervous system.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- DARPP-32 (Dopamine- and cAMP-Regulated Phosphoprotein) is a key regulator of intracellular signaling.
- The central nervous system form of DARPP-32 is primarily soluble.
- Parathyroid glands play a crucial role in calcium homeostasis.
Purpose of the Study:
- To identify and characterize DARPP-32 in bovine parathyroid glands.
- To investigate the localization and properties of parathyroid DARPP-32.
- To compare parathyroid DARPP-32 with its known forms in the central nervous system.
Main Methods:
- Immunoblot analysis of parathyroid tissue.
- Biochemical fractionation of cellular components.
- Metabolic labeling with mevalonolactone.
- Immunocytochemical localization studies.
Main Results:
- A 32 kDa DARPP-32 protein was identified in bovine parathyroid tissue.
- Parathyroid DARPP-32 was predominantly found in a particulate fraction, resistant to salt and carbonate washes.
- Metabolic labeling confirmed isoprenylation of parathyroid DARPP-32.
- Immunocytochemistry revealed DARPP-32 localized to cytoplasmic vesicles, with Protein Phosphatase-1 gamma concentrated at the plasma membrane.
Conclusions:
- A distinct, membrane-associated form of DARPP-32 exists in bovine parathyroid glands.
- This parathyroid DARPP-32 is isoprenylated and tightly bound to intracellular membranes.
- This contrasts with the predominantly soluble form found in the central nervous system, suggesting tissue-specific regulation and function.