Purification and characterization of a basic lysophospholipase in germinating barley

Area of Science:

• Plant Biochemistry
• Enzymology
• Glycoprotein characterization

Background:

• Lysophospholipids are key components in plant cell membranes and storage structures.
• Understanding enzymes involved in lysophospholipid metabolism is crucial for plant development, particularly during germination.
• Barley (Hordeum vulgare) seeds contain significant reserves, and their germination involves complex biochemical processes.

Purpose of the Study:

• To isolate and characterize lysophospholipase enzymes from germinating barley seeds.
• To determine the enzymatic properties, including molecular weight, isoelectric point, and substrate specificity.
• To elucidate the potential role of these enzymes in barley seed germination.

Main Methods:

• Enzyme isolation utilizing the basic, lipophilic, and carbohydrate-containing nature of the target activity.
• Isoelectric focusing for determining isoelectric point (pI).
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for molecular weight determination before and after deglycosylation.
• Enzyme kinetics assays (Km, Vmax) using lysophosphatidylcholine as a substrate.
• Stability studies in the presence of mercaptoethanol.

Main Results:

• Isolation of at least three forms of barley lysophospholipase with molecular weights of 40,000 and 41,000 Da.
• All forms exhibited an isoelectric point (pI) of 8.8 and contained 10-12% carbohydrate.
• Deglycosylation yielded a common polypeptide of 36,000 Da.
• The enzyme is sensitive to sulfhydryl reagents but stable for over 3 months at 4°C with mercaptoethanol.
• The most active enzyme showed a Km of 30 µM and Vmax of 200 µmol/min/mg for lysophosphatidylcholine.
• Specific activity was 20-fold higher than animal lysophospholipases.
• Enzyme exhibited specificity for lysophosphatidylcholine with saturated C16 or unsaturated C18 fatty acid chains.

Conclusions:

• Barley seeds possess multiple, distinct lysophospholipases with significant glycosylation.
• These enzymes are highly efficient catalysts for specific lysophospholipids found in barley starch inclusion complexes.
• The characterized properties suggest a vital role for these lysophospholipases in mobilizing lipid reserves during barley germination.