Brown adipose tissue Ca2+-ATPase: uncoupled ATP hydrolysis and thermogenic activity.
In this report a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) was identified in rats brown adipose tissue. Electrophoretic analysis of brown fat microssomal protein yields a 110-kDa band that is reactive to SERCA 1 antibody but is not reactive to SERCA 2 antibodies. Nevertheless, the kinetics properties of the brown fat SERCA differ from the skeletal muscle SERCA 1 inasmuch they manifest a different Ca2+ affinity and a much higher degree of ATPase/Ca2+ uncoupling. A SERCA enzyme is not found in white fat. Fatty acids promoted Ca2+ leakage from brown fat vesicles. The heat released during ATP hydrolysis was -24.7 kcal/mol when a Ca2+ gradient was formed across the vesicles membrane and -14.4 kcal/mol in the absence of a gradient. The data reported suggest that in addition to storing Ca2+ inside the endoplasmic reticulum, the Ca2+-ATPase may represent a source of heat production contributing to the thermogenic function of brown adipose tissue.
de Meis
Leopoldo
L
Instituto de Ciências Biomédicas, Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, RJ 21941-590, Brazil. demeis@bioqmed.ufjr.br
D002001:Adipose Tissue, Brown / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology; D006358:Hot Temperature; D006868:Hydrolysis; D007700:Kinetics; D018482:Muscle, Skeletal / Q000201:enzymology; D011817:Rabbits; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013816:Thermodynamics
D005227:Fatty Acids; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium