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Blood–Brain Barrier Protein and Phosphorylation and Dephosphorylation
Author(s) -
Pardridge William M.,
Yang Jing,
Eisenberg Jody
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb05534.x
Subject(s) - phosphoprotein , dephosphorylation , phosphorylation , chemistry , protein phosphorylation , blood–brain barrier , biochemistry , biophysics , biology , microbiology and biotechnology , central nervous system , endocrinology , phosphatase , protein kinase a
Capillaries in vertebrate brain have unique permeability properties that make up the blood–brain barrier (BBB). Although it is known that capillaries are innervated by nerve endings of intracerebral origin and that brain capillary function is likely acutely regulated by neuronal inputs, the possible mechanisms of neuronal regulation of capillary function are at present unknown. One possible mode of regulation is via the phosphorylation of brain capillary proteins. The present studies characterize, for the first time, the major phosphoproteins in the bovine brain capillary using both intact bovine brain capillaries and plasma membrane fractions from bovine brain capillaries. The patterns of endogenous phosphorylation of capillary proteins are compared to similar patterns obtained with synaptosomal (P 2 ) fractions from bovine brain. The major findings of this study are: (a) The activity of protein phosphorylation in brain capillaries is localized almost exclusively to the capillary plasma membrane, and is nearly comparable to the activity of protein phosphorylation in synaptosomal membranes. (b) A major phosphoprotein doublet in the capillary fraction comigrates on a sodium dodecyl sulfate gel with a major phosphoprotein doublet of approximate molecular weight of 80K in the synaptosomal fraction, and the latter is presumed to be synapsin I; in dephosphorylation assays the synaptosomal 80K phosphoprotein doublet is not subject to measurable dephosphorylation, whereas the capillary 80K doublet is subject to rapid dephosphorylation, and is essentially completely dephosphorylated within 5 s at 0°C. (c) A prominent triplet of phosphoproteins with molecular weight of 50–55K is present in the capillary fraction, and is not present in the synaptosomal fraction; thus, this 50—55K triplet of phosphoproteins appears specific for brain capillaries. In summary, these studies provide the basis for future investigations of a protein phosphorylation paradigm in regard to the rapid control of brain capillary function by brain.