Spermidine biosynthesis during germination and subsequent vegetative growth of Bacillus megaterium spores

Spermidine biosynthesis was extremely low early in germination of Bacillus megaterium spores and the spermidine level remained constant. Rapid synthesis began after 130 min and thereafter accounted for the increase in spermidine level which began at this time. Biosynthesis was greatly (>84%) diminished by exogenous spermine or spermidine. Arginine and ornithine were both converted efficiently into spermidine, but arginine was the more immediate precursor as shown by isotope competition studies and by the absence of ornithine decarboxylase and the presence of arginine decarboxylase. Exogenous putrescine was not incorporated into spermidine, although it was taken up rapidly and degraded.

Regulatory effects of polyamines on membrane-bound acetylcholinesterase

The effects of putrescene, spermidine and spermine on membrane-bound acetylcholinesterase from human erythrocyte ;ghosts' and the solubilized enzyme of the electric organ of the electric eel were studied by kinetic methods. Measurements were made by using a photometric method which made it possible to record the enzyme reaction in the steady-state phase. Substrate-concentration-dependent activation and inhibition of acetylcholinesterase by polyamines is similar to that by Na(+), K(+), Ca(2+), Mg(2+) and certain quaternary and bisquaternary amines. The kinetics suggest an allosteric reaction mechanism. On the basis of the kinetic results a role for the polyamines as modulators of synaptic acetylcholinesterase is proposed.

Hyperglycaemia produced by the polyamines spermine and spermidine

1 Intravenous injection of rabbits with the polyamines spermine (10-30 mg/kg) and spermidine (50-90 mg/kg) produced hyperglycaemia.2 Given by intraventricular injection, spermine and spermidine gave rise to hyperglycaemia in doses 250-500 times smaller than those effective intravenously.3 Intraventricular injections of the polyamines also produced hyperglycaemia in rats. Adrenal demedullation abolished the response.4 In the rabbit, the hyperglycaemia resulting from intraventricular injection of polyamines was abolished in reserpine-treated animals. Anaesthesia had no effect on the response unless accompanied by anoxia, when the response was potentiated.5 Intracisternal injections of the polyamines in rabbits were less effective than intraventricular injections in that doses about four times larger were required to elicit an equivalent response.

Replication of colicin E1 plasmid DNA in cell extracts. Origin and direction of replication

The structures of molecules of colicin E1 plasmid DNA that were in the process of being replicated in vitro were examined electron microscopically. Circular molecules containing a loop of approximately 7% of the length of the molecules were the major class of replicating molecules. The location of the loop was determined by treating the molecules with restriction endonuclease EcoR1, which introduced one unique double-strand break in the colicin E1 plasmid DNA molecules. The loops had a specific location with two branch points at approximately 17 and 24% of the molecular length from the endonuclease-sensitive site. Molecules with a larger loop were observed with a preparation labeled with 5-bromodeoxyuridine and enriched for these molecules. One of the branch points in these molecules was located at approximately 17% of the molecular length from the endonuclease-sensitive site independent of the size of the loops. These results indicate that the origin of replication of the plasmid DNA is located within the small loop and the replication proceeds unidirectionally. The molecules that had completed a round of replication had the monomeric twisted circular structure.

Spermidine in hormone-dependent differentiation of mammary gland in vitro

Stiulation of milk-protein synthesis in mouse mammary epithelium in vitro requires insulin, hydrocortisone, and prolactin. The requirement for hydrocortisone can be replaced by spermidine. The possibility that spermidine mediates the effect of glucocorticoid is also supported by the observation that the cellular spermidine concentration increases before the accelerated synthesis of casein and alpha-lactalbumin.

Replication of colicin E1 plasmid DNA in cell extracts. II. Selective synthesis of early replicative intermediates

The major products of colicin E1 plasmid DNA synthesis in cell extracts are completely replicated molecules and a class of molecules containing newly synthesized small DNA fragments. The addition of 10% glycerol and/or 2 mM spermidine to extracts blocks synthesis of completely replicated molecules while enhancing synthesis of molecules containing newly synthesized DNA fragments. The latter molecules, which contain on the average two DNA fragments of approximately 6 S, are early replicative intermediates for synthesis of completely replicated molecules. Synthesis of the intermediates is sensitive to rifampicin and depends on RNA synthesis. RNA components are linked to the 6S DNA molecules.

Heterotrophic nature of the cell-free protein-synthesizing system from the strict chemolithotroph, Thiobacillus thiooxidans

A cell-free protein-synthesizing system prepared from the strict chemolithotroph, Thiobacillus thiooxidans, was similar to that of heterotrophs. The poly-U directed system had a temperature optimum of 37 C, but in the presence of spermidine (3 mM) the optimum shifted to 45 C. Although growth of the chemolithotroph occurs only in acid conditions, the pH optimum for the cell-free system was pH 7.2. The endogenous-directed activity in the presence or absence of spermidine was maximal at pH 7.8. Spermidine had a stimulatory effect; however, this effect was dependent on the magnesium and tris(hydroxymethyl)aminomethane (Tris) concentrations. At low Tris concentrations (10 mM), spermidine (3 to 5 mM) could completely replace magnesium. When the Tris concentration was increased (50 mM), spermidine could not replace magnesium. Supernatant and ribosomal fractions from T. thiooxidans were exchanged with those of Bacillus thuringiensis and Escherichia coli, and the ribosomal fraction from the chemolithotroph gave good to moderate stimulation when exchanged with the supernatant from the heterotrophs. On the other hand, the supernatant from T. thiooxidans gave good stimulation when mixed with ribosomes from B. thuringiensis but poor activity with ribosomes from E. coli. Both supernatant and ribosomal fractions prepared from stationary phase extracts of T. thiooxidans were inactive in the cell-free system.