The reaction of serpins with proteinases involves important enthalpy changes.
When active serpins are proteolytically inactivated in a substrate-like reaction, they undergo an important structural transition with a resultant increase in their conformational stability. We have used microcalorimetry to show that this conformational alteration is accompanied by an important enthalpy change. For instance, the cleavage of alpha(1)-proteinase inhibitor by Pseudomonas aeruginosa elastase, Staphylococcus aureus V8 proteinase, or papain and that of antithrombin by leukocyte elastase are characterized by large enthalpy changes (DeltaH = -53 to -63 kcal mol(-1)). The former reaction also has a large and negative heat capacity (DeltaC(p)() = -566 cal K(-1) mol(-1)). In contrast, serpins release significantly less heat when they act as proteinase inhibitors. For example, the inhibition of pancreatic elastase, leukocyte elastase, and pancreatic chymotrypsin by alpha(1)-proteinase inhibitor and that of pancreatic trypsin and coagulation factor Xa by antithrombin are accompanied by a DeltaH of -20 to -31 kcal mol(-1). We observe no heat release upon proteolytic cleavage of inactive serpins or following inhibition of serine proteinases by canonical inhibitors or upon acylation of chymotrypsin by N-trans-cinnamoylimidazole. We suggest that part of the large enthalpy change that occurs during the structural transition of serpins is used to stabilize the proteinase in its inactive state.
Boudier
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Laboratoire d'Enzymologie, INSERM Unité 392, Université Louis Pasteur de Strasbourg, F-67400 Illkirch, France.
Bieth
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JG
D000818:Animals; D000991:Antithrombins / Q000737:chemistry; D002417:Cattle; D002918:Chymotrypsin / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D019272:Leukocyte Elastase / Q000737:chemistry; D010196:Pancreatic Elastase / Q000737:chemistry; D010206:Papain / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D015843:Serpins / Q000737:chemistry*; D013211:Staphylococcus aureus / Q000201:enzymology; D013696:Temperature; D013816:Thermodynamics
D000991:Antithrombins; D007093:Imidazoles; D010455:Peptides; D015843:Serpins; C037552:cinnamoylimidazole; D002918:Chymotrypsin; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; D010206:Papain