Comparative properties of genetically defined peptidases in maize

Area of Science:

• Biochemistry
• Plant Science
• Enzymology

Background:

• Maize (Zea mays) possesses various peptidases crucial for protein metabolism.
• Understanding these enzymes aids in comprehending plant physiological processes.

Purpose of the Study:

• To purify and characterize aminopeptidase isozymes (AMP1-AMP4) and an endopeptidase (ENP) from maize.
• To compare their biochemical properties, including molecular weight, substrate specificity, and inhibition profiles.

Main Methods:

• Purification using ammonium sulfate fractionation, ion-exchange chromatography (DEAE-Sephadex), gel filtration (Sephadex G-150), and hydroxylapatite chromatography.
• Molecular weight determination via gel filtration and SDS-PAGE.
• Substrate specificity analysis using naphthylamide derivatives and dipeptides.
• Enzyme inhibition studies with various metal ions and chemical reagents.

Main Results:

• Four aminopeptidases (AMP1-AMP4) and one endopeptidase (ENP) were successfully purified.
• Distinct substrate specificities were observed among the aminopeptidases.
• Molecular weights ranged from 61,000 to 92,000 Da, with AMP2 also estimated at 88,000 Da by SDS-PAGE.
• Aminopeptidases showed sensitivity to Zn2+, Cu2+, Hg2+, and p-mercuribenzoate, with differential inhibition by 1,10-phenanthroline.
• AMP4 showed similarities to barley and pea aminopeptidases.

Conclusions:

• Maize contains multiple aminopeptidase isozymes with distinct catalytic properties.
• The characterized peptidases exhibit varied responses to inhibitors, suggesting different active site characteristics.
• AMP4 shares biochemical traits with homologous enzymes from other plant species, indicating conserved functions.