The chemical structure of the reactive group of esterases

The action of diisopropyl phosphorofluoridate and other anticholinesterases on amino acids

“…Ashbolt & Rydon, 1952), especially since such side chains have been indicated as being involved in the active centres of both cholinesterase (Wilson & Bergmann, 1950) and chymotrypsin (Sizer, 1945); there are, however, several major pieces of evidence which stand in the way of this obvious conclusion. First, O-phosphorylserine a-id peptides of O-phosphorylserine have been isolated from hydrolysates of DFP-inhibited enzymes (Schaffer, May & Summerson, 1953Cohen, Oosterbaan & Warringa, 1954, 1955Schaffer, Harshmann, Engle & Drisko, 1955;Schaffer, Engle, Simet, Drisko & Harshmann, 1956;Turba & Grundlach, 1955;Oosterbaan, Kunst & Cohen, 1955; Oosterbaan, Warringa & Jansz, 1955), although it is recognized that this is not proof of primary attack at a serine side chain (cf. Jandorf et al 1955).…”

The reactivation of phosphorylated chymotrypsin

“…The present paper describes the complete reactivation of phosphorylated chymotrypsin by oximes and hydroxamic acids. The results necessitate some modification of views on the mechanisms for chymotryptic hydrolysis which have been proposed recently (Cunningham, 1957;Dixon & Neurath, 1957a;Davies & Green, 1958). EXPERIMENTAL…”

“…Chymotrypsin, like most other enzymes with esterase activity, is inactivated by combination with organophosphates (Balls & Jansen, 1952). The inactive phosphorylated enzyme is relatively stable in water but hydroxylamine and picolinohydroxamic acid will restore the activity by nucleophilic displacement of the enzyme from the phosphoryl residue (Cunningham, 1954;Jandorf, Crowell & Levin, 1955). The only reported kinetic study of this process is by Cunningham (1954) on reactivation with hydroxylamine, but his conclusions as to mechanism are open to criticism as, at best, only about 30 % of the original enzymic activity could be recovered.…”

The kinetics of reactivation, by oximes, of cholinesterase inhibited by organophosphorus compounds

“…The action of nucleophilic reagents (e.g. water, amines and anions) on diethyland diisopropylphosphorochloridates (RO)2P<01 has been studied by Dostrovsky & Halmann (1953), who found that although the relative rate of reaction depended to some extent upon the precise structure of the reagent, the diethyl compound was normally 5-10 times as reactive as the diisopropyl compound. Hackley et al (1955) have reported that hydroxamic acids react about 20 times as rapidly with Sarin as with DFP.…”

“…the pH-ChE activity curve (Wilson & Bergmann, 1950) and the photo-oxidation experiments of Weil, James & Buchert (1953)], that this phosphorylation occurs at the ring N of a histidine molecule. OR", If this group were the hydroxyl of serine then this would explain the isolation of serine phosphate on hydrolysis of ChE or chymotrypsin inhibited with DFP (Schaffer, May & Summerson, 1953, 1954Cohen, Oosterbaan, Warringa & Jansz, 1955). Davison (1955) only gives half-lives for the reactivation by aqueous hydrolysis at 370 of dimethylphosphoryl ChE and not the total reactivation obtained.…”