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Preferential tritium labelling of binding site residues in alpha chymotrypsin by exposure of the 1,3‐ 3 H‐diisopropylphosphoryl derivative to tritiated hydrogen sulfide
Author(s) -
White Frederick H.
Publication year - 1975
Publication title -
journal of labelled compounds
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0022-2135
DOI - 10.1002/jlcr.2590110103
Subject(s) - chemistry , tritium , labelling , tritiated water , ligand (biochemistry) , radiolysis , residue (chemistry) , histidine , radiochemistry , stereochemistry , receptor , enzyme , biochemistry , radical , physics , nuclear physics
When alpha chymotrypsin, labelled with a heavily tritiated diisopropylphosphoryl ( 3 HDIP) group on the serine residue at position 195, was exposed to tritiated hydrogen sulfide ( 3 HSH) under dry conditions, an incorporation of 3 H occurred that favored residues close to the binding site. The reaction mechanism remains unclear. A direct transfer of 3 H from the ligand is ruled out, al t hough 3 H in this position as well as in 3 HSH is essential for the labelling reaction. It is shown that the reaction does not involve self‐radiolysis. It is suggested that the reaction may instead be related to an observed instability of 3 H within the ligand, possibly through a free radical mechanism.