Synthesis of the mitogenic S-[2,3-bis(palmitoyloxy)propyl]-N-palmitoylpentapeptide from Escherichia coli lipoprotein

The N-terminal pentapeptide of the lipoprotein from the outer membrane of Escherichia coli was obtained by coupling S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-cysteine to O-tert-butylseryl-O-tert-butyl-seryl-asparaginyl-alanine tert-butyl ester followed by deprotection with trifluoroacetic acid. The tetrapeptide was built up from alanine tert-butyl ester with N-9-fluorenylmethyloxycarbonyl protected amino acids. S-[2,3-Bis(palmitoyloxy)propyl]-N-palmitoylcysteine was obtained from N,N'-dipalmitoylcystine di-tert-butyl ester via reduction to the thiol, and S-alkylation with racemic 3-bromo-1,2-propanediol followed by esterification with palmitic acid in the presence of dicyclohexylcarbodiimide/dimethylaminopyridine and deprotection with trifluoroacetic acid. The compounds were characterized unequivocally by 13C-NMR and mass spectra. The diastereomers of S-[2,3-bis(palmitoyloxy)propyl]-N-palmitoylcysteine tert-butyl ester with opposite configuration at the propyl-C-2 atom could be separated on a silica-gel column.     

Melittin and a chemically modified trichotoxin form alamethicin-type multi-state pores

The bee venom constituent, melittin, is structurally and functionally related to alamethicin. By forming solvent-free planar bilayers of small area (approx. 100 microns 2) on the tip of fire-polished glass pipettes we could observe single melittin pores in these membranes. An increase in the applied voltage induced further non-integral conductance levels. This indicates that melittin forms multi-level pores similar to those formed by alamethicin. Trichotoxin A40, an antibiotic analogue of alamethicin, also induces a voltage-dependent bilayer conductivity, but no stable pore states are resolved. However, chemical modification of the C-terminal molecule part by introduction of a dansyl group leads to a steeper voltage-dependence and pore state stabilization. Comparing structure and activity of several natural and synthetic amphiphilic polypeptides, we conclude that a lipophilic, N-terminal alpha-helical part of adequate length (dipole moment) and a large enough hydrophilic, C-terminal region are sufficient prerequisites for voltage-dependent formation of multi-state pores.     

ATP-dependence of 125I-insulin binding by rat soleus muscle

Muscle ATP levels were lowered by incubating rat soleus muscles under anaerobic conditions, or in the presence of 2:4-dinitrophenol (0.5 mM), EDTA (5 mM) or mannitol (400 mM). 125I-insulin binding, measured under equilibrium conditions at 25 degrees C, was reduced by 49-71% in ATP-depleted muscles. Insulin binding was also determined using two other procedures which minimized internalization of 125I-insulin: these were (a) 5 min at 25 degrees C, and (b) 24 h at 3 degrees C. Under these conditions, 125I-insulin binding was reduced by 28-55% in ATP-depleted muscles. These results confirm that in soleus muscle the effect of ATP-depletion on 125I-insulin binding is actually concerned with the binding step itself and not merely a reflection of ATP-dependent internalization of the bound hormone.     

High-performance liquid chromatography of coproporphyrin isomers.

A reversed-phase system is described for the simultaneous isocratic separation of coproporphyrin I, II, III and IV isomers. The retention behaviour of coproporphyrin I and III is studied in detail. The method is suitable for both analytical and semi-preparative separation.     

Distribution of Fusarium in some British soils

Soil fusaria from various areas in and around Surrey were estimated on medium selective forFusarium. 4 species ofFusarium, F. episphaeria. F. oxysporum, F. roseum andF. solani were detected.F. roseum was the most widely distributed species and present in highest numbers. Among 3 cultivars of this species obtained, non-pathogenic clones of “Culmorum” was always present. The other 3 species ofFusarium were less widely distributed and occurred in lower numbers, withF. solani being the most restricted in distribution and present in very small populations. NoFusarium was recorded for soils from natural field vegetation (except grass areas) and forests.     

Two high affinity estrogen binding proteins of different specificity in the immature rat uterus cytosol

The presence of two high affinity estrogen binding proteins in the uterine cytosol of the immature rat has been observed.Besides the 8 S cytosol estrogen $\text{receptor}$, there is a 4–5 S fraction binding estradiol and estrone with a large capacity. In fact, the two binding systems have a different affinity for estradiol and estrone, the receptor binding more the former and the 4–5 S fraction more the latter. Exposure of the cytosol to specific anti-α₁-Fetoprotein antibodies suppresses a large part of the 4–5 S binder, if not the totality. Moreover the estrogen binding 4–5 S fraction decreases with increasing age until puberty, while the $\text{receptor}$ increases. These results suggest therefore that the estradiol-estrone binding 4–5 S peak of the uterine cytosol is mainly made up of Estradiol Binding Plasma Protein-α₁-Fetoprotein (EBP-AFP). Also they confirm that “cytosol” should be taken as an operational fraction which may include extracellular components.During the course of these experiments, it has been observed that the increase of the estradiol $\text{receptor}$ is more rapid than the other uterine cytosol proteins until the 8th day, and that there is a second period of growth when it follows the development of the uterus and of the animal, as if it had reached a constant number of binding sites per cell.     

Hypermagnesaemia in Presence of Magnesium Depletion in Acute-on-chronic Renal Failure

A patient with renal failure developed hypermagnesaemia, with confusion, drowsiness, and dysarthria. Nevertheless, the dietary magnesium content was low, and investigation showed actual intracellular depletion of magnesium. The cause of this state is not known, though it is presumably connected with a failure to maintain the normal concentration gradient of magnesium across the cell wall. The clinical state and the serum magnesium level returned to normal after treatment with calcium gluconate.