To determine which structural characteristics of membrane phospholipids influence adenylate cyclase activity, we measured basal and sodium fluoride‐ or forskolin‐stimulated activity in a murine fibroblast cell line,i.e., Balb/c3T3 cells grown in media supplemented with fetal calf serum (FCS), lipid‐depleted FCS (LD‐FCS) or LD‐FCS complexed with different phosphatidylcholine (PC) molecular species. Cells grown in the presence of LD‐FCS showed a substantial decrease in their basal and NaF‐stimulated adenylate cyclase activities; however, their forskolin‐stimulated activity was not altered, suggesting that the enzyme's catalytic site is not affected by changes in membrane lipids. Media supplemented with different LD‐FCS/PC complexes were shown to prevent the LD‐FCS‐mediated reduction of basal and NaF‐stimulated adenylate cyclase activity to different extents. Addition ofcis‐9‐16∶1/cis‐9‐16∶1,cis‐9‐18∶1/cis‐9‐18∶1 orcis‐9‐18∶1/cis‐9,12‐18∶2sn‐glycerophosphocholine (GPC) completely restored adenylate cyclase activity, whilecis‐11‐18∶1/cis‐11‐18∶1 GPC was not effective and only a partial recovery was observed with 16∶0/16∶0, 16∶0/cis‐9‐18∶1 andtrans‐9‐18∶1 GPC. Considering the structural features of these seven PC molecular species, the findings suggest that an optimal lipid environment is conferred to the enzyme by the presence of thecis double bonds, each located in Δ9 position of the PC acyl chains. The limited effect ofcis‐9‐16∶1/cis‐9‐18∶1 GPC andcis‐9‐18∶1/cis‐9‐16∶1 GPC suggests that an equal length of the terminal hydrocarbon chains extending bevond the Δ9 double bonds is also important. Moreover, complete restoration of adenylate cyclase activity in cells exposed to 16∶0/cis‐9,12‐18∶2 GPC suggests that twocis‐9,12 double bonds located on the same chain are as effective as twocis‐9 double bonds each located on two different chains of PC. As the four double bonds of 16∶0/cis‐5,8,11,14‐20∶4 GPC had no effect, a mere increase in the number of double bonds seems insufficient to build an optimal lipid microenvironment for the enzyme.
Effect of phosphatidylcholine structure on the adenylate cyclase activity of a murine fibroblast cell line / L. Calorini; G. Mugnai; A. Mannini; S. Ruggieri. - In: LIPIDS. - ISSN 0024-4201. - ELETTRONICO. - 28:(1993), pp. 727-730. [10.1007/BF02535994]
Effect of phosphatidylcholine structure on the adenylate cyclase activity of a murine fibroblast cell line.
CALORINI, LIDO;MUGNAI, GABRIELE;MANNINI, ANTONELLA;RUGGIERI, SALVATORE
1993
Abstract
To determine which structural characteristics of membrane phospholipids influence adenylate cyclase activity, we measured basal and sodium fluoride‐ or forskolin‐stimulated activity in a murine fibroblast cell line,i.e., Balb/c3T3 cells grown in media supplemented with fetal calf serum (FCS), lipid‐depleted FCS (LD‐FCS) or LD‐FCS complexed with different phosphatidylcholine (PC) molecular species. Cells grown in the presence of LD‐FCS showed a substantial decrease in their basal and NaF‐stimulated adenylate cyclase activities; however, their forskolin‐stimulated activity was not altered, suggesting that the enzyme's catalytic site is not affected by changes in membrane lipids. Media supplemented with different LD‐FCS/PC complexes were shown to prevent the LD‐FCS‐mediated reduction of basal and NaF‐stimulated adenylate cyclase activity to different extents. Addition ofcis‐9‐16∶1/cis‐9‐16∶1,cis‐9‐18∶1/cis‐9‐18∶1 orcis‐9‐18∶1/cis‐9,12‐18∶2sn‐glycerophosphocholine (GPC) completely restored adenylate cyclase activity, whilecis‐11‐18∶1/cis‐11‐18∶1 GPC was not effective and only a partial recovery was observed with 16∶0/16∶0, 16∶0/cis‐9‐18∶1 andtrans‐9‐18∶1 GPC. Considering the structural features of these seven PC molecular species, the findings suggest that an optimal lipid environment is conferred to the enzyme by the presence of thecis double bonds, each located in Δ9 position of the PC acyl chains. The limited effect ofcis‐9‐16∶1/cis‐9‐18∶1 GPC andcis‐9‐18∶1/cis‐9‐16∶1 GPC suggests that an equal length of the terminal hydrocarbon chains extending bevond the Δ9 double bonds is also important. Moreover, complete restoration of adenylate cyclase activity in cells exposed to 16∶0/cis‐9,12‐18∶2 GPC suggests that twocis‐9,12 double bonds located on the same chain are as effective as twocis‐9 double bonds each located on two different chains of PC. As the four double bonds of 16∶0/cis‐5,8,11,14‐20∶4 GPC had no effect, a mere increase in the number of double bonds seems insufficient to build an optimal lipid microenvironment for the enzyme.
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