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Apparent induction, kinetic and physical properties of the multiple species of ornithine decarboxylase, forms A and B, in the kidney and liver of hormone-treated rat Janzen, Andrea K.


Ornithine decarboxylase occurs in the kidney and liver of control and hormone treated rats as two ionic forms, designated ODC A and B in order of elution by DEAE-Sepharose chromatography. These studies were designed to better characterize the multiple forms of ODC and to investigate the functions and possible origins of ODC A and B in growth hormone, prolactin and/or dexamethasone stimulated tissue. The two species of ODC existed in separate and distinct proportions in control rat kidney and liver. Within the kidney and liver of growth hormone, prolactin and dexamethasone stimulated rats, the proportions of ODC A and B were altered, reflecting the increased half-life of ODC B. In growth hormone-stimulated animals, form B had an increased half-life of 25 minutes in the kidney and 60 minutes in the liver. Hormone stimulated rats were also given either LiC1, actinomycin D orputrescine, which decreased total ODC activity. The ODC A:B ratio was altered in some instances, but only within the kidney. In these cases, the enhanced proportion and most likely the stability of the B form of ODC was inhibited or removed, as in the response of ODC to LiC1 in the stimulated kidney. Within the liver, there was no alteration of the A:B ratio. Possibly, the liver uses different signalling or regulatory mechanisms. ODC B did not have any kinetic advantage over A in either the kidney or liver of growthhormone-treated rats, as Km°rn and Vmax values did not differ significantly between forms A and B in either case. The charge separation of ODC A and B from the kidney and liver was shown to be dependent on the state of phosphorylation based on the evidence that prior treatment of supernatant containing ODC with alkaline phosphatase resulted in the elution of active ODC A only by DEAE chromatography. Finally, ODC A and B did not differ in molecular weight (-48kD) as seen on an SDS-PAGE gel. In growth hormone-treated rats, ODC showed complex responses in terms of activity orkinetics. Not only did the ratio of liver ODC A and B not respond to lithium, actinomycin or putrescine treatment, but there was evidence of multiple species of ODC within forms A and B having different kinetic and half-life properties.

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