Extraction and Partial Characterization of the Glycine Decarboxylase Multienzyme Complex from Pea Leaf Mitochondria

Abstract

Glycine decarboxylase has been successfully solubilized from pea (Pisum sativum) leaf mitochondria as an acetone powder. The enzyme was dependent on added dithiothreitol and pyridoxal phosphate for maximal activity. The enzyme preparation could catalyze the exchange of CO₂ into the carboxyl carbon of glycine, the reverse of the glycine decarboxylase reaction by converting serine, NH₄⁺, and CO₂ into glycine, and ¹⁴CO₂ release from [1-¹⁴C]glycine. The half-maximal concentrations for the glycine-bicarbonate exchange reaction were 1.7 millimolar glycine, 16 millimolar NaH¹⁴CO₂, and 0.006 millimolar pyridoxal phosphate. The enzyme (glycine-bicarbonate exchange reaction) was active in the assay conditions for 1 hour and could be stored for over 1 month. The enzymic mechanism appeared similar to that reported for the enzyme from animals and bacteria but some quantitative differences were noted. These included the tenacity of binding to the mitochondrial membrane, the concentration of pyridoxal phosphate needed for maximum activity, the requirement for dithiothreitol for maximum activity, and the total amount of activity present. Now that this enzyme has been solubilized, a more detailed understanding of this important step in photorespiration should be possible.