Glyoxylate transamination in intact leaf peroxisomes
1Biology Department, University of South Carolina, Columbia, South Carolina 29208.
Plant Physiology
|May 1, 1984
Summary
Spinach and oat leaf peroxisomes show amino acid transamination during photorespiration. Serine, glutamate, and alanine compete for glyoxylate, impacting glycine production.
Area of Science:
- Plant biochemistry and molecular biology
- Photosynthesis and photorespiration research
- Enzyme kinetics and metabolic pathways
Background:
- Peroxisomes play a crucial role in photorespiration, a process linked to photosynthesis.
- Glyoxylate transamination is a key step in photorespiration, involving amino acids.
- Understanding the substrate specificity and regulation of these enzymes is vital.
Purpose of the Study:
- To investigate the transamination of glycolate with serine, glutamate, and alanine in spinach and oat leaf peroxisomes.
- To determine the relative contributions of these amino acids to glyoxylate transamination.
- To elucidate the competitive interactions between these amino acids and their impact on photorespiration.
Main Methods:
- Assay of alpha-keto acid formation from intact spinach and oat leaf peroxisomes incubated with glycolate and amino acids.
- Analysis of transamination activity at varying substrate concentrations (glycolate and amino acids).
- Assessment of competitive inhibition between different amino acid substrates.
- Quantification of amino acid content in leaf extracts.
Main Results:
- Transamination activity saturated at 1 mM glycolate and 1 mM of each amino acid in spinach peroxisomes.
- Relative transamination rates in spinach: serine (40%), glutamate (30%), alanine (30%); in oats: serine (60%), glutamate (23%), alanine (17%).
- Mutual inhibition observed between the amino acids due to glyoxylate competition; competitive inhibition at the active site occurred between glutamate and alanine.
- Changes in relative amino acid concentrations altered their transamination rates.
Conclusions:
- Serine, glutamate, and alanine are significant substrates for glyoxylate transamination in spinach and oat leaf peroxisomes.
- The relative contribution of each amino acid to photorespiration is concentration-dependent and subject to competitive interactions.
- Enzyme kinetics reveal specific competitive inhibition patterns, highlighting the complex regulation of this metabolic pathway.
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