Dihydroxyacetone Phosphate Reductase in Plants

Publisher Website
Google Scholar
Abstract
Two forms of dihydroxyacetone phosphate reductase are present in spinach [Spinacia oleracea] soybean [Glycine max], pea [Pisum sativum] and mesophyll cells of corn [Zea mays] leaves. An improved homogenizing medium was developed to measure this activity. The enzyme was detectable only after dialysis of the 35 to 70% saturated (NH4)2SO4 fraction and the two forms were separated by chromatography on either DEAE cellulose or Sephacryl S-200. About 80% of the reductase was one form in the chloroplast and the rest was a second form in the cytosol as determined by chromatography and by fractionation of subcellular organelles. The amount of activity detectable in the chloroplast fraction was 10.7 micromoles of dihydroxyacetone phosphate reductase per hour milligram chlorophyll from spinach leaves and 4.9 from pea leaves. The chloroplast from eluted first from DEAE cellulose and, being smaller, it eluted second from Sephacryl S-200. Activity of the chloroplast form was stimulated 3- to 5-fold by the addition of 1 millimolar dithiothreitol or 5 microgram reduced Escherichia coli thioredoxin or 4 micrograms spinach thioredoxin to the assay mixture. This stimulation was not observed with monothiols. Activity of the cytosolic form was not affected by either reduced thioredoxin or dithiothreitol.