ENGINEERING ASCARIS HEMOGLOBIN OXYGEN-AFFINITY IN SPERM WHALE MYOGLOBIN - ROLE OF TYROSINE B10

The contribution to oxygen stabilization of a tyrosine residue in topo logical position (B10) has been studied in sperm whale myoglobin by si multaneous replacement of residues at positions (B10), (E7) and (E10) as suggested by analysis of the sequence of high oxygen affinity hemog lobins, such as that of the nematode Ascaris suum. Kinetic and equilib rium experiments with the gaseous ligands oxygen and carbon monoxide s how that indeed the introduction of tyrosine (B10), together with repl acement of the distal histidine (E7) with glutamine, is associated wit h a large decrease in the oxygen dissociation rate constant. Our resul ts are consistent with the possible formation in the distal pocket of two hydrogen bonds with the iron-bound oxygen.