A HEME-PROTEIN-BASED OXYGEN-SENSING MECHANISM CONTROLS THE EXPRESSIONAND SUPPRESSION OF MULTIPLE PROTEINS IN ANOXIA-TOLERANT TURTLE HEPATOCYTES

The O-2 sensitivity of protein expression was assessed in hepatocytes from the western painted turtle. Anoxic cells consistently expressed p roteins of 83.0, 70.4, 42.5, 35.3, and 16.1 kDa and suppressed protein s of 63.7, 48.2, 36.9, 29.5, and 17.7 kDa. Except for the 70.4-kDa pro tein, this pattern was absent during aerobic incubation with 2 mM NaCN , suggesting a specific requirement for O-2. Aerobic incubation with C o2+ or Ni2+ if inreased expression of the 42.5-, 35.3-, and 16.1-kDa p rotein bands which was diminished with the heme synthesis inhibitor 4, 6-dioxoheptanoic acid. Proteins suppressed in anoxia were also suppres sed during aerobic incubation with Co2+ Or Ni2+ but this was not relie ved by 4,6-dioxoheptanoic acid. The anoxia- and Co2+/Ni2+ induced expr ession of the 42.5-, 35.3-, and 16.1-kDa protein bands was antagonized by 10% CO; however, with the exception of the 17.7-kDa protein, this was not found for any of the O-2- or Co2+/Ni2+-suppressed proteins. An oxia-induced proteins were compared with proteins expressed during hea t shock. Heat shock proteins appeared at 90.2, 74.8, 63.4, 25, and 15. 5 kDa and were of distinct molecular masses compared with the anoxia-i nduced proteins. These results suggest that O-2-sensing mechanisms are active in the control of protein expression and suppression during an oxia and that, in the case of the 42.5-, 35.3-, 17.7-, and 16.1-kDa pr oteins, a conformational change in a ferro-heme protein is involved in transducing the O-2 signal.