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Studies on the temperature-dependent autoinhibition of human plasma kallikrein I
Abstract:
At 37 degrees C, human plasma kallikrein I follows Michaelis-Menten behaviour and exhibits a normal linear relationship between the initial velocity of hydrolysis of Ac-Pro-Phe-Arg-OMe,HCl and enzyme concentration in the range 0--150 pM. At temperatures of 30 degrees C and below substantial deviations from linearity are observed over the same enzyme concentration range. The temperature-dependent autoinhibition of kallikrein I activity is reversible and is not due to low-molecular-weight endogenous inhibitors or cofactors. The kinetic effect is apparently due to aggregation and can be abolished by the addition of sodium deoxycholate.
Insights
Human plasma kallikrein I activity is linear with enzyme concentration at 37°C but deviates at lower temperatures. This reversible autoinhibition, linked to enzyme aggregation, can be reversed by sodium deoxycholate.
Area of Science:
- Biochemistry
- Enzymology
- Protein Chemistry
Background:
- Human plasma kallikrein I (HPK I) is a key enzyme in the kallikrein-kinin system.
- Understanding HPK I kinetics is crucial for its physiological and pathological roles.
- Temperature-dependent enzyme activity can significantly impact experimental results.
Purpose of the Study:
- To investigate the kinetic behavior of human plasma kallikrein I across different temperatures.
- To elucidate the mechanism behind observed deviations from linearity at lower temperatures.
- To identify methods for reversing temperature-dependent autoinhibition.
Main Methods:
- Enzyme kinetic assays using Ac-Pro-Phe-Arg-OMe,HCl as substrate.
- Varying incubation temperatures (37°C, 30°C, and below).
- Assessing enzyme concentration-velocity relationships and the effect of sodium deoxycholate.
Main Results:
- HPK I exhibited Michaelis-Menten kinetics and a linear enzyme-velocity relationship at 37°C (0-150 pM enzyme concentration).
- Substantial deviations from linearity were observed at 30°C and below.
- The autoinhibition was reversible, not due to inhibitors/cofactors, and abolished by sodium deoxycholate, suggesting aggregation.
Conclusions:
- Temperature significantly influences HPK I kinetics, leading to autoinhibition below 37°C.
- Enzyme aggregation appears to be the cause of this temperature-dependent autoinhibition.
- Sodium deoxycholate can effectively reverse the autoinhibition, indicating its potential use in maintaining HPK I activity.