scholarly journals Effects of CoA and acyl-CoA on Ca2+-permeability of endoplasmic-reticulum membranes from rat liver

1995 ◽  
Vol 306 (3) ◽  
pp. 703-708 ◽  
Author(s):  
G T Rich ◽  
J G Comerford ◽  
S Graham ◽  
A P Dawson
Keyword(s):  
Fatty Acids ◽  
Membrane Fusion ◽  
Rat Liver ◽  
Liver Microsomes ◽  
Rat Liver Microsomes ◽  
Short Term ◽  
Esterified Fatty Acids ◽  
Chain Acyl ◽  
Microsomal Membranes ◽  
Long Chain

We have studied the effects of CoA and palmitoyl-CoA on Ca2+ movements and GTP-dependent vesicle fusion in rat liver microsomes. (1) Inhibition of membrane fusion by CoA depends on esterification of CoA to long-chain acyl-CoA using endogenous non-esterified fatty acids. (2) Binding of long-chain acyl-CoA to microsomal membranes is inhibited by BSA, which also relieves inhibition of membrane fusion. (3) Under conditions where acyl-CoA binding is inhibited, CoA causes increased Ca2+ accumulation, apparently by decreasing the Ca2+ leak rate. (4) Conversely, palmitoyl-CoA, in the presence of BSA, causes Ca2+ efflux. (5) The decrease in Ca(2+)-permeability caused by CoA does not depend on the presence of ATP or GTP, and is irreversible in the short term. (6) Using 14C-labelled CoA we show that CoA derivatives can be formed from endogenous components of microsomal membranes in the absence of ATP. (7) The results are interpreted in terms of a Ca(2+)-permeability which is controlled by CoA and/or long-chain acyl-CoA esters.

scholarly journals Subcellular distribution and characteristics of ciprofibroyl-CoA synthetase in rat liver. Its possible identity with long-chain acyl-CoA synthetase

1992 ◽  
Vol 284 (1) ◽  
pp. 283-287 ◽  
Author(s):  
L Amigo ◽  
M C McElroy ◽  
M N Morales ◽  
M Bronfman
Keyword(s):  
Rat Liver ◽  
Subcellular Distribution ◽  
Liver Microsomes ◽  
Mitochondrial Fraction ◽  
Rat Tissues ◽  
Rat Liver Microsomes ◽  
Freezing And Thawing ◽  
Chain Acyl ◽  
Related Proteins ◽  
Long Chain

The subcellular distribution and characteristics of ciprofibroyl-CoA synthetase were studied in rat liver and compared with those of long-chain acyl-CoA synthetase (palmitate as substrate) which, as already known, is distributed among mitochondria, microsomes and peroxisomes. Upon differential centrifugation, the subcellular distribution of ciprofibroyl-CoA synthetase followed closely that of palmitoyl-CoA synthetase and was specifically inactivated in the mitochondrial fraction by freezing and thawing, a behaviour already described for palmitoyl-CoA synthetase. Both enzyme activities were found to co-purify through several steps from rat liver microsomes. By using a partially purified enzyme, the activation of ciprofibrate to its acyl-CoA ester followed Michaelis-Menten kinetics with an apparent Km of 0.63 +/- 0.1 mM. Ciprofibroyl-CoA synthetase was competitively inhibited by 25 and 50 microM-palmitic acid. Higher concentrations of the fatty acid resulted in a mixed type of inhibition. Conversely, ciprofibrate up to 0.5 mM was found to inhibit competitively palmitoyl-CoA synthetase, whereas higher concentrations also resulted in a mixed inhibition. The highest activity of ciprofibroyl-CoA synthetase was found in fat and liver homogenates. The distribution of the enzyme in different rat tissues was similar to that of palmitoyl-CoA synthetase. The present results suggest that long-chain acyl-CoA synthetase and ciprofibroyl-CoA synthetase activities reside in identical or closely related proteins.

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