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Microsomal methionine aminopeptidase: properties of the detergent-solubilized enzyme
Abstract:
A methionine aminopeptidase (MAP) found in rat liver microsomes behaves as membrane-bound enzyme. Triton-solubilized MAP when chromatographed on DEAE-cellulose columns was separated from other microsomal arylamidases. The enzyme hydrolyzes N-terminal methionine from methionyl-lysyl-bradykinin (Met-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) being then characterized as a typical aminopeptidase. It also shows preferential arylamidase activity upon Met-2-naphthylamide. MAP was activated by 2-mercaptoethanol and inhibited by p-hydroxymercuribenzoate. Contrarily to other well characterized aminopeptidases, MAP was not affected by EDTA, puromycin or bestatin. Altogether these data suggest that MAP is a unique microsomal enzyme distinct from other previously described aminopeptidases. It could be involved in the removal of methionine from nascent peptides during protein synthesis.
Insights
Researchers identified a unique rat liver microsomal enzyme, methionine aminopeptidase (MAP), that removes N-terminal methionine from peptides. This enzyme differs from other aminopeptidases and may play a role in protein synthesis.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Microsomal fractions contain various enzymes, including arylamidases.
- Methionine aminopeptidases (MAPs) are crucial for protein processing.
- Characterization of specific enzyme functions is vital for understanding cellular mechanisms.
Purpose of the Study:
- To isolate and characterize a methionine aminopeptidase (MAP) from rat liver microsomes.
- To determine the enzymatic properties and substrate specificity of the identified MAP.
- To differentiate this MAP from other known aminopeptidases and elucidate its potential biological role.
Main Methods:
- Enzyme solubilization using Triton and separation via DEAE-cellulose chromatography.
- Hydrolysis assays using methionyl-lysyl-bradykinin and Met-2-naphthylamide substrates.
- Enzyme activity modulation studies using activators (2-mercaptoethanol) and inhibitors (p-hydroxymercuribenzoate), and assessment of effects of EDTA, puromycin, and bestatin.
Main Results:
- A membrane-bound methionine aminopeptidase (MAP) was successfully isolated from rat liver microsomes.
- The enzyme specifically hydrolyzes N-terminal methionine from peptide and arylamide substrates.
- MAP activity is enhanced by 2-mercaptoethanol and inhibited by p-hydroxymercuribenzoate, but unaffected by EDTA, puromycin, or bestatin.
Conclusions:
- Rat liver microsomal MAP is a unique enzyme, distinct from previously characterized aminopeptidases.
- Its unique properties suggest a specialized function within the microsomal environment.
- This enzyme may be involved in the removal of methionine from nascent peptides during protein synthesis.