Modification of transplasma membrane oxidoreduction by SV40 transformation of 3T3 cells

Abstract

Transformation of 3T3 cells by SV40 virus changes the properties of the transplasma membrane electron transport activity which can be assayed by reduction of external ferric salts. After 42 h of culture and before the growth rate is maximum, the transformed cells have a much slower rate of ferric reduction. The change in activity is expressed both by change in Km and Vmax for ferricyanide reduction. The change in activity is not based on surface charge effect or on tight coupling to proton release or on intracellular NADH concentration. With transformation by SV40 virus infection the expression of transferrin receptors increases, which correlates with greater diferric transferrin stimulation of the rate of ferric ammonium citrate reduction in transformed SV40-3T3 cells than in 3T3 cells.

The Oxidative Function of Diferric Transferrin

“…All the assay procedures done after 1988 with diferric transferrin tested for adventious iron show significant reduction of the diferric transferrin or stimulation of NADH oxidase although the rates are clearly higher if extra iron is present. This is consistent with the stimulation of reduction when ferric ammonium citrate is added along with transferrin as shown in Table 2 [31]. An involvement of the transferrin receptor in activation of the iron reduction may be indicated since the rate with transferrin present can increase over the rate with the same amount of iron [31].…”

“…This is consistent with the stimulation of reduction when ferric ammonium citrate is added along with transferrin as shown in Table 2 [31]. An involvement of the transferrin receptor in activation of the iron reduction may be indicated since the rate with transferrin present can increase over the rate with the same amount of iron [31]. …”

“…The second assay for reduction of diferric transferrin by NADH and plasma membrane measures the formation of ferrous bathophenanthroline disulfonate (BPS) at 535 nm [23]. This procedure has also been used to show diferric transferrin reduction at the surface of several different types of cells [31–34]. The use of BPS to show the reduction of iron in differic transferrin has been objected to on the basis that BPS effectively raises the redox potential of the ferric transferrin so that it can be reduced by NADH [35].…”

“…Measurement of adventious loosely bound iron using ascorbate as a reductant and BPS to measure formation of ferrous BPS showed that the most active preparations contained up to 1 u mole of loosely bound iron [37] per u mole transferrin. After 1988, diferric transferrin was checked for adventious iron [31, 33, 37]. All the assay procedures done after 1988 with diferric transferrin tested for adventious iron show significant reduction of the diferric transferrin or stimulation of NADH oxidase although the rates are clearly higher if extra iron is present.…”