The regulation of porphobilinogen oxygenase and porphobilinogen deaminase activities in rat bone marrow under conditions of erythropoietic stress.
Porphorbilinogen oxygenase (EC 4.2.1.24) was associated with the microsomal fraction of bone marrow in normal rats and in rats submitted to erythropoietic stress, while porphobilinogen deaminase (EC 4.3.1.8) of the same origin was present in the cytosol. An NADPH-dependent electron-donor system for the oxygenase was also present in the microsomes of the bone marrow. Under conditions of erythropoietic stress caused by hypoxia, the activities of both enzymes were found to be inversely correlated. While the oxygenase showed minimum activity between the 4th and 8th day of hypoxia, porphobilinogen deaminase reached its maximum activity during this period. After the 8th day of hypoxia, oxygenase activity increased while deaminase activity decreased. The NADPH-dependent electron-transport system necessary for the microsomal oxygenase activity was largely inactivated after the 10th day of hypoxia, while oxygenase activity was not affected. The particulate porphobilinogen oxygenase could be solubilized from the bone marrow microsomes with 1% deoxycholate or 0.5 M KCl. In addition, the oxygenase was also released by freezing and thawing the microsomes isolated from bone marrow of rats which had been submitted to an erythropoietic stress (hypoxia or phenylhydrazine). The enzyme solubilized with deoxycholate or KCl showed a high molecular weight form and a low molecular weight form (Mr 25 000). The former could be transformed into the latter either by treatment with 2 M KCl or by succinylation. When the oxygenase was solubilized by freezing and thawing a third molecular weight form (Mr 50 000) also appeared. The solubilized enzyme could be succinylated without loss of its catalytic activity, while the membrane-bound enzyme could not be succinylated.
Frydman
R B
RB
Tomaro
M L
ML
Sburlati
A
A
Gutnisky
A
A
D000642:Ammonia-Lyases / Q000378:metabolism*; D000818:Animals; D001853:Bone Marrow / Q000201:enzymology*; D002850:Chromatography, Gel; D004920:Erythropoiesis; D005260:Female; D011163:Hydroxymethylbilane Synthase / Q000378:metabolism*; D000860:Hypoxia / Q000201:enzymology; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D008970:Molecular Weight; D010658:Phenylglyoxal / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D006899:Mixed Function Oxygenases; C022429:porphobilinogen oxygenase; D011163:Hydroxymethylbilane Synthase; D000642:Ammonia-Lyases; D010658:Phenylglyoxal