TY - JOUR
T1 - Positive surface charge inhibition of phospholipase A2 in mixed monolayer systems
AU - Willman, Cheryl
AU - Hendrickson, H. Stewart
N1 - Funding Information:
in part at the 19th West Central States Conference, Ames, Iowa, Nov. 5-6, 1976. was supported by Grant NS 11777 from Institutes Health. to whom correspondence
PY - 1978/11
Y1 - 1978/11
N2 - Inhibition of pancreatic phospholipase A2 by surface-active local anesthetics was recently reported by this laboratory to be due to enzyme-anesthetic interaction in the subphase and surface effects. In order to study surface effects in the absence of subphase effects, a long-chain tetracaine analog which was completely insoluble in the subphase, dimethylaminoethyl p-decoxybenzoate, was synthesized. To determine if inhibition was due to the positive surface charge of the analog or some other effect related to structure, the analog's inhibitory effects were compared with those of octadecylamine. Analog-didecanoyl lecithin (PC) monolayers showed nonideal mixing as evidenced by a condensing effect, while octadecylamine-didecanoyl PC monolayers showed ideal mixing. The apparent pK′a of octadecylamine-dioctanoyl PC micelles (1:4) was 9.9, while that of the analog-dioctanoyl PC micelles (1:4) was 7.6. At pH values where both amines were fully protonated, inhibition of both porcine pancreatic and Crotalus adamanteus phospholipase A2 on the mixed films was maximal and similar (94-97%). Inhibition decreased with increasing pH and decreasing surface charge on both mixed films and at pH values where both amines were 50% protonated, inhibition was half-maximal. At pH 8.5, where the analog was unprotonated, no inhibition was observed. Thus, inhibition of phospholipase A2 appears to be due to a positive surface charge alone rather than any effects related to anesthetic structure or spacing in the monolayer.
AB - Inhibition of pancreatic phospholipase A2 by surface-active local anesthetics was recently reported by this laboratory to be due to enzyme-anesthetic interaction in the subphase and surface effects. In order to study surface effects in the absence of subphase effects, a long-chain tetracaine analog which was completely insoluble in the subphase, dimethylaminoethyl p-decoxybenzoate, was synthesized. To determine if inhibition was due to the positive surface charge of the analog or some other effect related to structure, the analog's inhibitory effects were compared with those of octadecylamine. Analog-didecanoyl lecithin (PC) monolayers showed nonideal mixing as evidenced by a condensing effect, while octadecylamine-didecanoyl PC monolayers showed ideal mixing. The apparent pK′a of octadecylamine-dioctanoyl PC micelles (1:4) was 9.9, while that of the analog-dioctanoyl PC micelles (1:4) was 7.6. At pH values where both amines were fully protonated, inhibition of both porcine pancreatic and Crotalus adamanteus phospholipase A2 on the mixed films was maximal and similar (94-97%). Inhibition decreased with increasing pH and decreasing surface charge on both mixed films and at pH values where both amines were 50% protonated, inhibition was half-maximal. At pH 8.5, where the analog was unprotonated, no inhibition was observed. Thus, inhibition of phospholipase A2 appears to be due to a positive surface charge alone rather than any effects related to anesthetic structure or spacing in the monolayer.
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U2 - 10.1016/0003-9861(78)90092-9
DO - 10.1016/0003-9861(78)90092-9
M3 - Article
C2 - 736568
AN - SCOPUS:0018159018
SN - 0003-9861
VL - 191
SP - 298
EP - 305
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 1
ER -