The structure of adenosine deaminase complexed with 6-hydroxyl- 1, 6-dihydropurine ribonucleo- 
side, a nearly ideal analogue of the transition state of catalysis, and the zinc cofactor, as deter- 
mined by crystallographic technique. Adenosine deaminase plays a central role in maintaining 
immune competence; impairment of its catalytic activity is associated with severe combined 
immunodeficiency (SCID), affecting both T and B lymphocytes. 
Research of David K. Wilson and Florante A. Quiocho. 
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