Abstract
With yeast-soluble inorganic pyrophosphatase, the heat released during PP(i) hydrolysis was -6.3 kcal/mol regardless of the KCl concentration in the medium. With the membrane-bound pyrophosphatase of corn vacuoles, the heat released varies between -23.5 and -7.5 kcal/mol depending on the KCl concentration in the medium and whether or not a H(+) gradient is formed across the vacuole membranes. The data support the proposal that enzymes are able to handle the energy derived from phosphate compound hydrolysis in such a way as to determine the parcel that is used for work and the fraction that is converted into heat.
Highlights
With yeast-soluble inorganic pyrophosphatase, the heat released during PPi hydrolysis was ؊6.3 kcal/mol regardless of the KCl concentration in the medium
The data support the proposal that enzymes are able to handle the energy derived from phosphate compound hydrolysis in such a way as to determine the parcel that is used for work and the fraction that is converted into heat (de Meis, L. (2001) J
The ability to modulate the conversion of energy into either heat or work varies depending on both the enzyme and the experimental conditions used. This was first observed with the sarco/endoplasmic reticulum Ca2ϩ-ATPases (SERCA),1 a family of membrane-bound ATPases that are able to translocate Ca2ϩ ion across the membrane by using the chemical energy derived from ATP hydrolysis. With these enzymes it was found that the heat released during ATP hydrolysis may vary from 10 to 30 kcal/mol depending on the SERCA isoform used and on whether or not a Ca2ϩ gradient is formed across the membrane [1,2,3,4,5,6,7,8,9,10]
Summary
With yeast-soluble inorganic pyrophosphatase, the heat released during PPi hydrolysis was ؊6.3 kcal/mol regardless of the KCl concentration in the medium. The ability to modulate the conversion of energy into either heat or work varies depending on both the enzyme and the experimental conditions used This was first observed with the sarco/endoplasmic reticulum Ca2ϩ-ATPases (SERCA), a family of membrane-bound ATPases that are able to translocate Ca2ϩ ion across the membrane by using the chemical energy derived from ATP hydrolysis. With these enzymes it was found that the heat released during ATP hydrolysis may vary from 10 to 30 kcal/mol depending on the SERCA isoform used and on whether or not a Ca2ϩ gradient is formed across the membrane [1,2,3,4,5,6,7,8,9,10]. We found that the amount of heat released during PPi hydrolysis varies depending on the enzyme used, but contrary to the proposal by Szoke et al [12], the amount of heat released by vacuolar PPase was larger than that measured with yeast-soluble PPase
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