Steroidal constituents of Solanum xanthocarpum

From the extract of the fruits of Solanum xanthocarpum (Solanaceae), five new steroidal compounds were isolated and characterized: 4α-methyl-24ξ-ethyl-5α-cholest-7-en-3β,22ξ-diol (1), 3β,22ξ-dihydroxy-4α-methyl-24ξ-ethyl-5α-cholest-7-en-6-one (2), 3β-benzoxy-14β,22ξ-dihydroxy-4α-methyl-24ξ-ethyl-5α-cholest-7-en-6-one (3), 3β-benzoxy-14α,22ξ-dihydroxy-4α-methyl-24ξ-ethyl-5α-cholest-7-en-6-one (4) and 3β-(p-hydroxy)-benzoxy-22ξ-hydroxy-4α-methyl-24ξ-ethyl-5α-cholest-7-en-6-one (5).     

Human-Mouse Hybrid Cell Lines and Susceptibility to Poliovirus : I. Conversion from Polio Sensitivity to Polio Resistance Accompanying Loss of Human Gene-Dependent Polio Receptors

A number of human-mouse somatic hybrid cell lines have been prepared, containing from 3 to 12 human biarmed chromosomes. These lines were susceptible to poliovirus type 1, producing viral yields comparable to those of the human parental cells. A small proportion of the cells of these lines survived the polio infection, and their progeny were solidly resistant to reinfection with the virus. Both sensitive and resistant hybrids produced virus following infection with viral ribonucleic acid, indicating that the cytoplasm of the resistant hybrids was able to support viral multiplication. Viral adsorption studies carried out at 4 C showed that the resistant sublines had negligible ability to adsorb the virus. It was concluded that the hybrid cells became resistant to polio through loss of the human chromosome bearing the gene for the receptor substance.     

Effect of guanidine on the squid giant synapse

Effects of guanidine on pre- and postsynaptic activities in the untreated or tetrodotoxin-treated squid giant synapses were examined by externally perfusing with various concentrations (423 mM, 42 mM, 21 mM, and 4.2 mM), or by iontophoretic injection of guanidine into the presynaptic terminal. In 423 mM guanidine (Na-free), the pre- and postsynaptic spikes together with PSP were completely abolished. In concentrations of 42 mM or lower of guanidine media the following changes related to the concentration used were observed: reduction of delayed rectification of both axon membranes without significant alteration of resting membrane resistances; a few millivolts decrease in the resting membrane potentials; small decrease in amplitude of pre- and post-synaptic spikes without marked increase of spike duration; enhancement of synaptic activity as manifested by increases in the amplitude and duration of the PSP. Iontophoretically injected guanidine also reduced delayed rectification of the presynaptic membrane. Input-output relation was modified in a way similar to externally applied guanidine and an “Off-PSP” was demonstrated shortly after application of an inside positive presynaptic polarization. Thus, a comparison of the augmentation of synaptic transmission by the extracellular and intracellularly applied guanidine demonstrates that the primary effect is at the presynaptic terminal.     

Influence of ionic environment on the relationship between pre- and postsynaptic potentials

The effects of various ions on the relationship between pre- and postsynaptic potentials were studied using untreated squid giant synapses, or those injected presynaptically with tetraethylammonium ions (TEA) in the presence of 10^?6 g/ml tetrodotoxin (TTX). The synaptic transfer function was, in general, augmented by increasing [Ca²⁺]₀ or by reducing [Mg²⁺]₀. Opposite results were found by lowering either [Na⁺]₀ or [Ca²⁺]₀, or by increasing [K⁺]₀ or [Mg²⁺]₀. When [Ca²⁺]₀ was removed, presynaptically applied depolarizations failed to produce both “On-” and “Off-PSP's.” Electrophoretically injected Ca²⁺ into the presynaptic terminal reduced synaptic transmission. The minimal level of presynaptic membrane potential produced by an applied outward current pulse, which suppressed On-PSP completely, averaged 106 mV inside positive (ranging between 52–205 mV from 12 preparations). The potential level was shifted more negatively on lowering [Ca²⁺]₀ and more positively in high [Ca²⁺]₀-media. However, altering the [Na⁺]₀ did not change the suppression level appreciably. Under these ionic circumstances the maximum amplitude of On-PSP, as well as Off-PSP, was markedly changed, but the level of the presynaptic depolarization required to evoke a maximum On-PSP appeared to be unchanged, and the average value was 50 mV from the resting membrane potential level. Although the data are only qualitative, they appear to support the “Ca hypothesis” for the transmitter release and its shut-off mechanism. Replacement of 423 mM Cl^? by Br^? or with isethionate did not affect synaptic transmission.     

Absence of demonstrable linkage of human genes for enzymes of the purine and pyrimidine salvage pathways in human-mouse somatic cell hybrids

A number of different reduced human-mouse hybrids have been analyzed for the presence of human enzymes of the purine and pyrimidine salvage pathways. Homologous mouse and human enzymes were characterized by isoelectric fractionation or gel electrophoresis, and the species of origin of the enzyme in hybrid clones was determined. Hybrids selected for one of the human enzymes, thymidine kinase, adenine phosphoribosyltransferase, or hypoxanthine phosphoribosyltransferase, were each found to contain the selected enzyme but not the other two. Neither human adenosine kinase nor human deoxycytidine (cytidine) deaminase was present in any of the hybrid clones. A human 5-nucleotidase was present in two hybrid clones containing human hypoxanthine phosphoribosyltransferase, but the genes for the two enzymes are not linked. The genes for the purine and pyrimidine salvage enzymes appear to be dispersed in the human genome.These investigations were aided by a grant from the National Cancer Institute.     

Plasmid-mediated lethality and plasmid multimer formation in an Escherichia coli recBC sbcBC mutant. Involvement of RecF recombination pathway genes

Apparent plasmid instability, i.e. progressive plasmid loss in a bacterial culture growing in the absence of selection for the plasmid, in an Escherichia coli recBC sbcBC mutant was investigated with two different ColE1 derivatives (pMB9 and pBR322) and a mini-F plasmid. The instability was most striking for pMB9 and much less, but still significant, for pBR322 and the mini-F. It was also dependent upon a subset of the genes involved in the RecF recombination pathway: in addition to the previously reported recA, recF and recJ mutations, a recO and a recQ mutation showed a total and a partial suppression, respectively, of the instability. Other recF-family mutations, recN and ruv, were without such an effect. Population analyses of the recBC sbcBC strain carrying pMB9 or the mini-F, as carried out by plating and Coulter counting, revealed marked loss of viability in plasmid-carrying cells, strongly implicating plasmid-mediated cell death in the apparent defect in plasmid maintenance. Analysis of intracellular plasmid DNA by pulsed-field gel electrophoresis combined with the in-agarose cell lysis technique showed that the instability was associated with the formation of plasmid multimers, with a good correlation between the degree of the instability and the amount of the multimers. The multimer formation was also dependent on the same subset of the RecF pathway genes as in the instability phenomenon. These results strongly suggest that the lethality is somehow caused by the multimer formation. Various DNase treatments of cell lysates showed that such multimers of pMB9 DNA comprised molecules of exonuclease-sensitive and exonuclease-resistant types. It was inferred that the former class, which showed electrophoretic mobilities corresponding to plain linear duplexes of approximately 200 x 10(3) to 2200 x 10(3) base-pairs, represented linear multimers possibly carrying circular structures at one end. The latter class, which remained in the origin, was thought to consist of circular multimers and/or linear multimers protected by circular structures at both ends against exonucleolytic attack.