Mutants of Escherichia coli K-12 were constructed such that each possessed one single major system for phosphate transport. A comparison of these strains showed that one of the systems (PIT) was fully constitutive, required no binding protein, and operated in spheroplasts. It permitted the complete exchange of intracellular phosphate with extracellular phosphate (or arsenate) and was completely inhibited by uncouplers. The other system, PST, was repressible by phosphate concentrations above 1 mM, required the phosphate-binding protein for full activity, and did not operate in spheroplasts. It catalyzed very little exchange between internal and external phosphate and was resistant to uncouplers. The maximal velocities attained by the two systems were approximately the same, but the affinity for phosphate in the PST system was greater by two orders of magnitude. In strains in which both systems were fully operative, the initial rates of uptake were nearly additive, and the systems appeared to interact with a common intracellular phosphate pool.

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The link between the cognitive deficit associated with Alzheimer type dementia and the loss of cholinergic function in the disease provides a basis for examining muscarinic agonists as potential therapeutic agents. This paper describes the design and synthesis of novel azabicyclic methyl esters as ligands for the muscarinic receptor. Replacement of the methyl ester by a 3-methyl-1,2,4-oxadiazole ring produces potent metabolically more stable muscarinic agonists capable of penetrating the central nervous system. These compounds generally show improved affinity relative to the corresponding methyl esters. 3-Methyl-1,2,4-oxadiazole 7b has an affinity 4 times that of acetylcholine. Receptor affinity is discussed in relation to the size and geometry of the azabicyclic ring and the electronic properties of the heteroaromatic ring.

When a strain (arcB-) of Escherichia coli, unable to synthesize the iron transport compound enterochelin, was transduced to tonB-, it became resistant to phage phi80 and simultaneously lost the growth response to enterochelin and the ability to transport its iron complex. However, enterochelin precursors (shikimate and 2,3-dihydroxybenzoate) still supported growth, via the synthesis of enterochelin. Dihydroxybenzoate was a better growth factor at a low concentration than it was at higher levels. The evidence suggests that tonB- strains lack an outer membrane component necessary both for the uptake of ferric-enterochelin and for the adsorption of phage phi80. Thus, although ferric-enterochelin cannot penetrate the cell surface from outside, the complex that is formed within the envelope is transported normally into the cell. The aroB-, tonB- mutant also lacked growth reponses to citrate and various hydroxamate siderochromes, which supported growth in the tonB+ parent strain via inducible transport systems for their ferric complexes. The aroB-, tonB- mutant was unable to transport iron in the presence of citrate, but the low-affinity uptake of uncomplexed iron and the transport of amino acids and phosphate were unimpaired. The tonB locus, thus, affects all the known active transport systems for iron, possibly indicating that they share some common outer membrane component.

Three mutant strains of Escherichwa coli have been isolated which are lacking ferric-enterochelin esterase activity. This enzyme catalyzes the hydrolysis of the enterochelin moiety of ferric-enterochelin to yield ultimately three molecules of N-2, 3-dihydroxybenzoylserine. The mutants (designated fes-) were shown to be unaffected in enterochelin biosynthesis, capable of enterochelin-mediated iron uptake, and able to utilize ferric-dihydroxybenzoylserine complexes normally. When grown under iron-deficient conditions, however, they showed an absolute requirement for added iron or citrate, a phenotype characteristic of mutants defective in some part of the enterochelin system of iron uptake. These results support the theory that iron, taken up by the cell as ferric-enterochelin is only available for general cell metabolism after hydrolysis of the ligand by enterochelin esterase. The three fes-strains were shown to be affected,in the B