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EFFECT OF SALTS ON THE PHYSICAL AND KINETIC PROPERTIES OF HUMAN PLACENTAL CHOLINE ACETYLTRANSFERASE
Author(s) -
Hersh Louis B.,
Peet Martha
Publication year - 1978
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1978.tb12402.x
Subject(s) - ionic strength , chemistry , choline acetyltransferase , protonation , enzyme , ionic bonding , salt (chemistry) , choline , biochemistry , inorganic chemistry , ion , organic chemistry , aqueous solution , biology , acetylcholine , endocrinology
— The effects of salt on the properties of human placental choline acetyltransferase have been examined. Increases in enzyme activity, thermal denaturation and susceptibility to proteolysis can be related to increases in ionic strength, rather than to specific salt effects. Increased ionic strength increases the maximal velocity (K m ) of the reaction, with no change in the kinetic parameter V max /K m (choline). The pH‐K m profile, measured over the range of 6.5–8.0, indicates the requirement of a dissociated acidic residue whose pKa is below 7.5 at high ionic strength, and a protonated residue whose pKa is above 7.5 at low ionic strength. It is proposed that the conformation of the enzyme is different at high ionic strength and at low ionic strength, and that these different conformational states of the enzyme result in different rate‐determining steps of the reaction.