U. Kim et al., PURIFICATION AND CHARACTERIZATION OF DOUBLE-STRANDED-RNA ADENOSINE-DEAMINASE FROM BOVINE NUCLEAR EXTRACTS, The Journal of biological chemistry, 269(18), 1994, pp. 13480-13489
The double-stranded RNA (dsRNA) adenosine deaminase (DRADA) deaminates
adenosine residues to inosines and creates I-U mismatched base pairs
in dsRNAs. Its involvement in RNA editing of glutamate-gated ion chann
el gene transcripts in mammalian brains has been proposed as one of th
e biological functions for this recently identified cellular enzyme. W
e purified a mixture of three forms, 93, 88, and 83 kDa, of bovine DRA
DA proteins, all likely to be active enzymes. We determined that DRADA
has a native molecular mass of approximately 100 kDa, suggesting that
the enzyme exists as a monomer. The purified enzyme was not inhibited
by 2'-deoxycoformycin, a transition state analog inhibitor of adenosi
ne deaminase and AMP deaminase, suggesting that the catalytic mechanis
m of DRADA might be different from that of other deaminases. DRADA bin
ds specifically to dsRNA with a dissociation constant of 0.23 nM for a
synthetic dsRNA, and the Michaelis constant is 0.85 nM. These values
indicate that DRADA has a much higher affinity for its substrate than
other deaminases such as adenosine deaminase and AMP deaminase. DRADA
may need this extremely high affinity to catalyze efficiently the modi
fication of relatively rare substrate RNAs in the cell nucleus.