Oxidation of protoporphyrinogen to protoporphyrin, a step in chlorophyll and haem biosynthesis. Purification and partial characterization of the enzyme from barley organelles.
The protoporphyrinogen-oxidizing enzyme from Triton X-100 extracts of the mitochondrial and etioplast fractions of etiolated barley was purified by using ion-exchange and hydroxyapatite chromatography. The purified enzyme from both organelle fractions exhibited a Km of 5 microM and was labile to mild heat and acidification. The pH optimum (5-6) and the substrate-specificity (mesoporphyrinogen was oxidized as rapidly as protoporphyrinogen) revealed properties very different from the protoporphyrinogen-oxidizing enzyme of rat liver or yeast mitochondria, which is specific for protoporphyrinogen as substrate. The purest fractions showed a polypeptide band corresponding to an Mr of approx. 36,000 on SDS/polyacrylamide-gel electrophoresis. This is the first purification and characterization of the enzyme from a plant, and indicates no readily detectable differences between the enzyme isolated from mitochondrial or etioplast fractions, although only the latter organelle has the capacity for both haem and chlorophyll synthesis.
Jacobs
J M
JM
Department of Microbiology, Dartmouth Medical School, Hanover, NH 03756.
Jacobs
N J
NJ
D002736:Chloroplasts / Q000201:enzymology; D002850:Chromatography, Gel; D002523:Edible Grain / Q000201:enzymology*; D001467:Hordeum / Q000201:enzymology*; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D010088:Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050768:Protoporphyrinogen Oxidase; D011524:Protoporphyrins / Q000378:metabolism; D013053:Spectrophotometry; D013379:Substrate Specificity
D011524:Protoporphyrins; C011539:protoporphyrinogen; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050768:Protoporphyrinogen Oxidase