Most living cells require potassium for growth and maintain a high intracellular concentration of that ion over a wide range of extracellular concen­ tration. The selectivity for potassium over sodium is determined by the transport systems which reside in the cytoplasmic membrane. It is a well established fact by now that the per­ meability of natural and artifical membranes for potassium is in...

Liposomes which have entrapped the metallochromic dye, arsenazo III, constitute a sensitive assay system for ionophoresis of divalent cations. By this means we have compared known calcium ionophores (A23187, ionomycin) with membrane phospholipids, fatty acids, prostanoids, and retinoids. Added at micromolar concentrations to preformed multilamellar liposomes (phosphatidylcholine 7:dicetyl phosp...

Chloroplasts contain the enzyme glutamine synthetase. Formation of glutamine by isolated chloroplasts is light-dependent and requires an intact outer envelope. Addition of exogenous glutamic acid, as well as nitrogen donors such as nitrite or ammonium, stimulate the synthesis of this amide. Photosynthetic generation of ATP satisfies the light requirement of glutamine synthesis. The process is s...

To solve two problems of Bergman stated in 1981, we construct a group G such that G contains a free noncyclic subgroup (hence, G satisfies no group identity) and G, as a group, is generated by its subsemigroup that satisfies a nontrivial semigroup identity.

Translocation of radioactive carbon from the fed part of a blade to the rest of the plant was impaired by a deficiency in phosphorus only when the level of phosphorus was low enough to decrease growth.Phosphorus deficiency decreased the percentage of inorganic phosphorus more than that of organic phosphorus, indicating little effect of phosphorus deficiency upon phosphorylation.Thus phosphorus ...