HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 297/5/R1460    most recent 90993.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by da Costa, D. C. F. Articles by Landeira-Fernandez, A. M. PubMed PubMed Citation Articles by da Costa, D. C. F. Articles by Landeira-Fernandez, A. M.

Articles

Thermogenic activity of the Ca²⁺-ATPase from blue marlin heater organ: regulation by KCl and temperature

Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Brazil

Submitted December 10, 2008 ; accepted in final form August 17, 2009

This work shows that vesicles derived from the blue marlin heater organ retain a sarcoplasmic reticulum (SR) Ca²⁺-ATPase that can interconvert different forms of energy. During the hydrolysis of ATP part of the energy is always converted into heat, and the other part can be converted into work (Ca²⁺ transport) or heat, depending on the temperature and the presence of KCl in the reaction medium. At 15°C, where KCl stimulates the activity approximately threefold, measurements of the amount of heat released per mole of ATP hydrolyzed (H^cal) show similar values (approximately –11 kcal/mol) in the presence or absence of a Ca²⁺ gradient. At 25°C, KCl activates the enzyme to the same extent as at 15°C, but inhibits the production of extra heat by SR Ca²⁺-ATPase when a Ca²⁺ gradient is built up across the membrane. The H^cal values found in the presence of a Ca²⁺-gradient were –26.2 ± 2.9 kcal/mol (n = 7) in control experiments and –16.1 ± 1.5 (n = 14) in the presence of 100 mM KCl. At 35°C, KCl has a smaller effect (1.5-fold) on activating the enzyme. Similar to SR Ca²⁺-ATPase from mammals, at this temperature the enzyme produces almost twice the amount of heat per mole of ATP hydrolyzed in the presence of a Ca²⁺ gradient and KCl has no effect at all on this increment. These data suggest that the marlin SR Ca²⁺-ATPase may play an important role in heater organ thermogenesis and that KCl has the potential for regulating the heat production catalyzed by the enzyme.

billfish; regional endothermy; SERCA1; Makaira nigricans