Chapter 8 191 ENZYMES R of substrate O…H—N HC HC C H….9 Threonine side chain of enzyme Serine side chain CH of enzyme Figure 8-12 Hydrogen bond interactions in the binding of a uridine substrate to ribo- nuclease. [After F M. Richards, H w Wyckoff, and N. Allewell. In The Neu rosciences: Second Study Program, FO Schmidt, ed( Rockefeller University Press,,1970),p.970