Characterization of adenosine binding proteins in human placental membranes

Miscellaneous · Sun Jan 01 00:00:00 EST 1989

OSTI ID:6414842

Hutchison, K A

We have characterized two adenosine binding proteins in human placenta. In membranes, one site is detected with ({sup 3}H) -N-ethylcarboxamidoadenosine (({sup 3}H)NECA). This site is similar to the adenosine A{sub 2} receptor. We call this site the adenosine A{sub 2}-like binding site. In detergent extracts, the second site is detected and has the characteristics of an adenosine A{sub 1} receptor. The soluble adenosine A{sub 2}-like binding site cannot be detected without a rapid assay. Binding to the adenosine A{sub 1} receptor with ({sup 3}H)-2-chloroadenosine and ({sup 3}H)NECA is time dependent, saturable, and reversible. Equilibrium displacement analysis with adenosine agonists reveals an A{sub 1} specificity: 2-chloroadenosine > R-phenylisopropyladenosine > 5{prime}-N-ethylcarboxamidoadenosine. The antagonist potency order is 1,3-diethyl-8-phenylxanthine > isobutylmethylxanthine > theophylline. Competition analysis of membranes with the A,-selective ligands ({sup 3}H)-cyclohexyladenosine ({sup 3}H) cylopentylxanthine revealed adenosine A{sub 1} agonist and antagonist potency orders. We have purified the adenosine A{sub 2}-like binding site. The adenosine A{sub 2}-like binding site is an ubiquitous major cellular protein. It is glycosylated, highly asymmetric, and acidic. The native protein is an homodimer with a subunit molecular mass of 98 kDa. The sedimentation coefficient and partial specific volume of the binding complex are 6.9 s and 0.698 ml/g, respectively. The Stokes' radius is 70 {Angstrom}. The native molecular mass of the detergent-protein complex is 230 kDa. The adenosine A{sub 2}-like binding site has an agonist potency order of 5'-N-ethylcarboxamidoadenosine > 2-chloroadenosine >> R-phenylisopropyladenosine and an antagonist potency order of isobutylmethylxanthine > theophylline >> 1,3-diethyl-8-phenylxanthine.

• Research Organization: Michigan Univ., Ann Arbor, MI (USA)
• OSTI ID: 6414842
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ADENOSINE
RECEPTORS
CHEMICAL COMPOSITION
BIOCHEMICAL REACTION KINETICS
CELL MEMBRANES
FRACTIONATION
PLACENTA
TIME DEPENDENCE
TRACER TECHNIQUES
TRITIUM COMPOUNDS
CELL CONSTITUENTS
FETAL MEMBRANES
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
KINETICS
MEMBRANE PROTEINS
MEMBRANES
NUCLEOSIDES
NUCLEOTIDES
ORGANIC COMPOUNDS
PROTEINS
REACTION KINETICS
RIBOSIDES
SEPARATION PROCESSES
550201* - Biochemistry- Tracer Techniques