TY - JOUR
T1 - The Allosteric Activation of Mammalian α‐Amylase by Chloride
AU - Levitzki, Alexander
AU - Steer, Michael L.
PY - 1974/1
Y1 - 1974/1
N2 - α‐Amylase from hog pancreas is shown to possess one binding site for Cl− per molecule of enzyme with a dissociation constant of 3 × 10−4 at 25 °C. The chloride anion functions as an activating effector increasing kcat 30‐fold towards either starch or p‐nitrophenylmaltoside. No change in Km for either substrate is seen. The other monovalent anions Br−, I−, NO2−, NO3−, ClO4−, SCN−, N3− and CNO− can substitute for chloride but their effect on kcat decreases as their anionic radius increases. Chloride binding induces a subtle conformational change in the enzyme reflected by the suppression of the exchange of 26 protons and a 240‐fold increase in the amylase‐Ca2+ binding constant from 8.3 × 108 to 2 × 1011 M−1. The conformational change is minor since it is not detected by circular dichroism, protein fluorescence or by specific probes attached to the enzyme. The ability of small structural changes to induce large catalytic acceleration is discussed.
AB - α‐Amylase from hog pancreas is shown to possess one binding site for Cl− per molecule of enzyme with a dissociation constant of 3 × 10−4 at 25 °C. The chloride anion functions as an activating effector increasing kcat 30‐fold towards either starch or p‐nitrophenylmaltoside. No change in Km for either substrate is seen. The other monovalent anions Br−, I−, NO2−, NO3−, ClO4−, SCN−, N3− and CNO− can substitute for chloride but their effect on kcat decreases as their anionic radius increases. Chloride binding induces a subtle conformational change in the enzyme reflected by the suppression of the exchange of 26 protons and a 240‐fold increase in the amylase‐Ca2+ binding constant from 8.3 × 108 to 2 × 1011 M−1. The conformational change is minor since it is not detected by circular dichroism, protein fluorescence or by specific probes attached to the enzyme. The ability of small structural changes to induce large catalytic acceleration is discussed.
UR - http://www.scopus.com/inward/record.url?scp=0015975824&partnerID=8YFLogxK
U2 - 10.1111/j.1432-1033.1974.tb03257.x
DO - 10.1111/j.1432-1033.1974.tb03257.x
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C2 - 4856205
AN - SCOPUS:0015975824
SN - 0014-2956
VL - 41
SP - 171
EP - 180
JO - European Journal of Biochemistry
JF - European Journal of Biochemistry
IS - 1
ER -