Zymogen-Enzyme Transformations. On the Mechanism of Activation of Prophospholipase A
| Autor: | Michel Lazdunski, Jean-Pierre Abita, Wim A. Pieterson, Pieter P. M. Bonsen, Gerard H. de Haas |
|---|---|
| Rok vydání: | 1972 |
| Předmět: |
Spectrophotometry
Infrared Protein Conformation Swine Stereochemistry Trypsinogen Phospholipase Aminopeptidases Biochemistry chemistry.chemical_compound Zymogen medicine Animals Trypsin Enzyme kinetics Pancreas Enzyme Precursors Phospholipase A Alanine Binding Sites biology Chemistry Tryptophan Active site Substrate (chemistry) Enzyme Activation Kinetics Optical Rotatory Dispersion Spectrometry Fluorescence Phospholipases Phosphatidylcholines biology.protein Calcium Spectrophotometry Ultraviolet medicine.drug |
| Zdroj: | European Journal of Biochemistry. 30:37-47 |
| ISSN: | 1432-1033 0014-2956 |
| Popis: | Transformation of prophospholipase A into phospholipase A is triggered by the tryptic hydrolysis of the Arg7-Ala8 bond of the zymogen. This bond is a better substrate for trypsin than the corresponding strategic bonds of other zymogens such as trypsinogen and chymotrypsinogen A or B: Km= 2.2 mM, kcat= 7 s−1 at pH 8, 1°C. Calcium ions which have an essential role in phospholipase catalysis play no role in prophospholipase activation. A comparative physico-chemical analysis of the zymogen and of the enzyme shows that activation produces only very limited changes in the overall folding of prophospholipase. A structural rearrangement occurs at the N-terminal end of the precursor. An excellent fluorescence reporter group to follow this conformational modification is the side-chain of tryptophan-3 (in phospholipase sequence) which passes from a polar to an apolar environment during activation. The α-amino group of alanine-1 (in the phospholipase sequence) which appears on activation is essential for enzyme activity. Selective chemical modification of this function by a number of reagents abolishes phospholipase activity. By analogy with the chymotrypsinogen-chymotrypsin and the proelastase-elastase transformations, it is proposed that the α-amino group is involved in the formation of a salt-bridge which stabilizes the adequate geometry of the active site. Evidences in favor of this hypothesis include the high pK and the low chemical reactivity of the α-amino group, together with the resistance of native phospholipase to aminopeptidase degradation. |
| Databáze: | OpenAIRE |
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