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Degradation of prolylleucylglycinamide (MIF) by mouse brain
Abstract:
Prolylleucylglycinamide (MIF) at 1.0 mM concentration and pH 7.0 was hydrolyzed by mouse brain homogenate at a rate of 140 nmol/mg protein/hr. Nearly all of this activity can be accounted for by the action of two enzymes, both of which cleave Pro and Leu sequentially from the N-terminus of MIF. At pH 7.0 the predominant enzyme is arylamidase, inhibited by puromycin (1 mM) and Mn2+ (2.5 mM). At pH 8.5, in the presence of Mn2+, a second enzyme with a higher potential activity (570 nmol/mg protein/hr) was observed. While the arylamidase is primarily localized in the cytosol, the Mn2+-stimulated enzyme is equally divided between soluble and particulate fractions. Because of its ability to cleave leucinamide, its high pH optimum, and its Mn2+ dependence, it can be classified as a leucine aminopeptidase (LAP). In its substrate specifically and its preference for Mn2+ over Mg2+ it resembles the LAP from connective tissue more than that from other sources.
Insights
Mouse brain homogenate contains two enzymes that hydrolyze Prolylleucylglycinamide (MIF). One is arylamidase at pH 7.0, and the other is a manganese-dependent leucine aminopeptidase (LAP) active at pH 8.5.
Area of Science:
- Biochemistry
- Enzymology
- Neuroscience
Background:
- Prolylleucylglycinamide (MIF) is a peptide found in biological systems.
- Enzymatic hydrolysis of peptides is crucial for protein turnover and signaling.
- Mouse brain homogenate contains various peptidases with distinct activities and localizations.
Purpose of the Study:
- To characterize the enzymes responsible for Prolylleucylglycinamide (MIF) hydrolysis in mouse brain homogenate.
- To determine the kinetic properties and cofactor requirements of these enzymes.
- To investigate the subcellular localization of the identified enzymes.
Main Methods:
- Enzyme activity assays using Prolylleucylglycinamide (MIF) as a substrate.
- Characterization of enzyme kinetics at different pH values and in the presence of inhibitors and metal ions (Mn2+, Mg2+).
- Subcellular fractionation to determine enzyme localization (cytosolic vs. particulate).
Main Results:
- Two enzymes were identified, sequentially cleaving Pro and Leu from MIF's N-terminus.
- At pH 7.0, arylamidase activity (140 nmol/mg protein/hr) was predominant, inhibited by puromycin and Mn2+.
- At pH 8.5 with Mn2+, a leucine aminopeptidase (LAP) showed higher activity (570 nmol/mg protein/hr) and was distributed between soluble and particulate fractions.
Conclusions:
- Mouse brain homogenate possesses distinct enzymatic activities for MIF hydrolysis.
- Arylamidase and a manganese-dependent LAP are the primary enzymes involved.
- The characterized LAP exhibits properties similar to connective tissue LAP, suggesting specific roles in the brain.