SUMMARYSex-linkage of phosphoglucomutase (PGM) is widespread in the Orthoptera. For each of three species studied (representing the two suborders), the specific activity of PGM in males (the heterogametic sex) is almost identical to that in females, providing direct evidence that the difference in gene dose of a sex-linked locus in males and females is compensated in the Orthoptera. The Orthoptera is only the third group for which compensation has been demonstrated. Dosage compensation has been investigated in three orders of insects: it is present in Orthoptera and Diptera but absent in Lepidoptera. It is postulated that dosage compensation arose or was present in related archopteran ancestors and has been secondarily lost in Lepidoptera, possibly in association with female heterogamety in this group.

Seven antagonists of the calcium-binding protein calmodulin were found to inhibit iron and transferrin uptake by reticulocytes. This inhibition could be completely accounted for by inhibition of the endocytosis and exocytosis of transferrin. When four of the antagonists were tested with the nucleated erythroid cells from the liver of the fetal rat, inhibition of iron uptake was also observed but at higher concentrations than required for the same degree of inhibition with reticulocytes. The tumor promoters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDB) were shown to increase the rates of iron and transferrin uptake by reticulocytes and fetal liver erythroid cells by accelerating the rates of transferrin endocytosis and exocytosis. Since these substances are known to stimulate the calcium-activated enzyme protein kinase C while calmodulin antagonists are inhibitory, it is concluded that this enzyme plays an important role in the endocytosis and intracellular cycling of transferrin, and iron uptake by immature erythroid cells. However, the possibilities that calmodulin is also involved or that the inhibitory effects of the calmodulin antagonists are due to nonspecific actions on the cell membrane cannot be excluded.