In addition to the labelling of erythrocytes with 5'Cr, Thompson et al (1981) studied the labelling with y9mTc. They observed, apart from interaction of both these isotopes with haemoglobin, the binding of y9mTc to some erythrocyte membrane proteins, namely spectrin. They also showed that only pentavalent technetium is capable of interaction with membrane proteins and that thiol compounds like 2-mercaptoethanol and dithiothreitol disrupt the bond.In our experiments we have studied the labelling of the erythrocyte membranes with "Mo and we found some strikingly similar features (Kselikova et al. 1980). Hexavalent "Mo did not bind as well as heptavalent 9ymTc. Only after molybdenum was reduced (preferably with ascorbic acid) was binding to erythrocyte membrane proteins observed. Spectrin appeared to be primarily involved in the labelling pattern. When we were looking for the optimal conditions of membrane proteins separation by SDS-PAGE we also checked for influence of 2-mercaptoethanol on the stability of the "Mo interaction with membrane proteins. We solubilized the suspension of ghosts obtained by hypotonic haemolysis with the solution of 8 M ureas, 2%) SDS, 2% 2-mercaptoethanol(l: 1 ) and then we heated this solution for 3 min in the boiling water bath. For comparison, in some experiments we omitted 2-mercaptoethanol in the solubilizing medium. This step had, however, unlike in case of y y m T~ little effect on the extent of the erythrocyte membrane proteins binding ability. Even in the presence of a reducing agent as much as one third of the total applied radioactivity is associated with spectrin after membrane proteins separation by SDS-PAGE. Hence we can conclude that yyMo binding spectrin is far more resistent under reductive conditions as compared with y9mTc.

This study describes the interaction of molybdenum with blood components. Molybdenum-99 was added to blood, and after four washings, 3% of the total radioactivity was found in red cells. More specifically, the radioactivity was determined to be associated with the cell membrane.Molybdenum-99 in the +VI form did not interact with the human erythrocyte membrane; however, Mo(V) forms did interact. Of five different compounds, the highes uptake was observed with a brown Mo(V)-ascorbate complex generated from Mo(VI) and ascorbic acid in the molar ratio 1∶20. A membrane suspension of Mo-ascorbate-treated human erythrocytes was prepared and the solubilized proteins were separated on a polyacrylamide gel in the presence of sodium dodecyl sulfate (SDS). Molybdenum-99 binding to spectrin was demonstrated, as well as some minor interactions with membrane hemoglobin and bands 6 and 8.

Molybdenum in the form of its pentavalent complex binds primarily to spectrin when incubated with erythrocytes. Only the band 1 subunit is involved in this interaction thus indicating some structural differences between spectrin subunits.

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