Adenosine deaminase binding protein

Daddona, P. E., and Kelley, W. N., 1978, Human adenosine deaminase binding protein, /. Biol. Chem. 253 4617. 

To separate inactive adenosine deaminase from the remaining active enzyme, the protein, after the gel filtration on Sephadex G-25, is passed through a 9-(p-aminobenzyl)adenine-sepharose column (1.0 X 1-5 cml equilibrated with 0.1 M sodium phosphate at pH 8, or with 0.1 M NH4HCO3. The active adenosine deaminase binds to the column while the inactive enzyme passes through. The elution of the active enzyme is obtained by using 0.1 M sodium phosphate at pH 8, containing 4 mM guanylurea as a competitive enzyme inhibitor. 

Identification of proteins that bind to Z-DNA added one further step to the establishment of the presence of Z-DNA in vivo and its possible biological role. Herbert and Rich [22] demonstrated an in vitro assay system where one type of double-stranded RNA adenosine deaminase, called DRAD-binding Z-DNA. There are evidences that topoisomerase II from Drosophila, hiunan and calf thymus recognizes a number of DNA shapes, including Z-DNA [34,35]. Bloomfield and coworkers [36] have found that the condensation of plasmids is enhanced by Z-DNA conformation in d(CG)n repeats. The information related to B-Z transition [31], the effect of ligands on it [28,29] and X-ray crystal structure data [37,38] appear to suggest that the possible biological role of this polymorphic form of DNA will be soon established. 

Adenosine deaminase (ADA) is an amino hydrolase that catalyzes the deamination of adenosine and 2 -deoxyadenosine to inosine and 2 -deoxyinosine, respectively. High activity of ADA is seen in thymus and other lymphoid tissues. ADA has been shown in many different physical forms. A small form of the enzyme predominates in the spleen, stomach, and red blood cells, whereas the large form predominates in the kidney, liver, and skin fibroblasts. The small form of the catalytic subunit can be converted to the large form by complexing with a protein termed binding protein or complexing protein. 

Selective quenching allows also to put into evidence and to study a conformational change within a protein. ADAR2 (adenosine deaminase that acts on RNA) is a -80-kDa protein that efficiently deaminates the R/G site of GluR-B pre-mRNA sequences in vitro (O Connell et al. 1997). This enzyme has an RNA binding domain (RBD)l located in the C-terniinal catalytic domain. Deamination of adenosine (A) in the mRNA results in inosine (I) at that position. Because inosine is translated as guanosine (G), the editing reaction causes a functional A to G replacement. 

The enzyme is widely distributed in animal tissues and microorganisms and has been purified by classical methods from several sources. - Multiple forms, which differ for electrophoretic mobility and molecular weight, have been observed in animal tissues in some cases the origin of these forms is due to the binding of catalytically inactive peptides or proteins to adenosine deaminase molecules. Recently, we have prepared a specific adsorbent, 9-(p-aminobenzyl) adenine bound to Sepharose, which allows the rapid and quantitative purification of the enzyme from several sources independently from the physicochemical properties of the multiple forms. ... 

---