In Vitro Antimicrobial Activity and Human Pharmacology of Cephalexin, a New Orally Absorbed Cephalosporin C Antibiotic

Concentrations of cephalexin (an orally absorbed derivative of cephalosporin C) in serum and urine were determined in normal volunteers and patients. The in vitro antibacterial activity was also studied. All strains of group A β-hemolytic streptococci and Diplococcus pneumoniae were inhibited by 3.1 μg/ml. Of the Staphylococcus aureus strains, 88% were inhibited by 6.3 μg/ml, and 12.5 μg/ml was inhibitory for all S. aureus, 80% of Escherichia coli, 72% of Klebsiella-Aerobacter, and 56% of Proteus mirabilis strains. About 90 to 96% of E. coli, Klebsiella Aerobacter, and P. mirabilis strains were inhibited by 25 μg of cephalexin per ml. Pseudomonas and indole-positive Proteus strains proved to be quite resistant to cephalexin. Cephalexin was well absorbed after oral administration. A peak serum concentration of cephalexin of at least 5 μg/ml was achieved in each volunteer with 250 and 500-mg doses. A mean peak serum concentration of 7.7 μg/ml was achieved with 250-mg doses; 12.3μg/ml was achieved with 500-mg doses of antibiotic. Food did not interfere with absorption. Probenecid enhanced both the peak serum concentration and the duration of antibiotic activity in the serum. Over 90% of the administered dose was excreted in the urine within 6 hr. The mean peak serum concentration of cephalexin after an oral dose of 500 mg was adequate to inhibit all group A streptococci, D. pneumoniae, and S. aureus, 85% of E. coli, and about 40 to 75% of Klebsiella-Aerobacter and P. mirabilis strains. Levels of cephalexin in urine were adequate to inhibit over 90% of E. coli, and P. mirabilis and 80 to 96% of Klebsiella-Aerobacter strains.     

Uptake, distribution and binding of beryllium to organelles of the rat liver cell

1. Male rats were injected intravenously with amounts ranging from 0.08 to 111.0mumoles of [(7)Be]beryllium sulphate/kg. body wt. The distribution in the rat and the subcellular distribution of beryllium in the liver were determined. 2. Within the entire dose range a higher specific activity of beryllium was present in a mitochondrial fraction containing the lysosomes. Purification of this fraction confirmed that beryllium is taken up by lysosomes. 3. With doses approaching the LD(50), beryllium was also found in increasing amounts to be present in the liver cell nuclei. Beryllium also showed affinity towards isolated cell nuclei in vitro. Evidence is presented that they have one class of binding sites for beryllium. Mitochondria have less affinity for beryllium. 4. No evidence could be obtained of an affinity of beryllium for DNA or RNA by fractionation of nuclei and dialysis experiments. 5. The presence of beryllium in liver cell nuclei may be relevant to the effects of beryllium on nuclear structure and function.     

Conformational changes induced by the transforming amino acid substitution in the transmembrane domain of theneu oncogene-encoded p185 protein

Theneu oncogene is frequently found in certain types of human carcinomas and has been shown to be activated in animal models by nitrosourea-induced mutation. The activating mutation in theneu oncogene results in the substitution of a glutamic acid for a valine at position 664 in the transmembrane domain of the encoded protein product of 185 kda (designated p185), which, on the basis of homology studies, is presumed to be a receptor for an as yet unidentified growth factor. It has been proposed that activating amino acid substitutions in this region of p185 lead to a conformational change in the protein which causes signal transduction via an increase in tyrosine kinase activity in the absence of any external signal. Using conformational energy analysis, we have determined the preferred three-dimensional structures for the transmembrane decapeptide (residues 658–667) of the p185 protein with valine and glutamic acid at the critical position 664. The results indicate that the global minimum energy conformation of the decapeptide from the normal protein with Val at position 664 is an α-helix with a sharp bend (CD* conformation at residues 664 and 665) in this region, whereas the global minimum conformation for the decapeptide from the mutant transforming protein with Glu at position 664 assumes an all α-helical configuration. Furthermore, the second highest energy conformation for the decapeptide from the normal protein is identical to the global minimum energy conformation for the decapeptide from the transforming protein, providing a possible explanation why overexpression of the normal protein also has a transforming effect. These results suggest there may be a normal and a transforming conformation for theneu-encoded p185 proteins which may explain their differences in transforming activity.     

Cell-specific fatty acylation of proteins in cultured cells of neuronal and glial origin

Distinct sets of cellular proteins were labeled with [³H]myristic and [³H]palmitic acids in primary (rat neurons and astroglia) and continuous (murine N1E-115 neuroblastoma and rat C6 glioma) cell cultures derived from the nervous system. Both soluble and membrane proteins were modified by myristate in a hydroxylamine-stable (amide) linkage, while palmitoylated proteins were esterlinked and almost exclusively membrane bound. Chain elongation of both labeled fatty acids prior to acylation was observed, but no protein amide-liked [³H]myristate originating from [³H]palmitate was detected. Fatty acylation profiles differed considerably among most of the cell lines, except for rat astroglial and glioma cells in which myristoylated proteins appeared to be almost identical based on SDS gel electrophoresis. An unidentified 47 kDa myristoylated protein was labeled to a significantly greater extent in astroglial than in glioma cells; the expression of this protein could be related to transformation or development in cells of glial origin.     

Prebiotic synthesis of diaminopyrimidine and thiocytosine

The reaction of guanidine hydrochloride with cyanoacetaldehyde gives high yields (40–85%) of 2,4-diaminopyrimidine under the concentrated conditions of a drying lagoon model of prebiotic synthesis, in contrast to the low yields previously obtained under more dilute conditions. The prebiotic source of cyanoacetaldehyde, cyanoacetylene, is produced from electric discharges under reducing conditions. The effect of pH and concentration of guanidine hydrochloride on the rate of synthesis and yield of diaminopyrimidine were investigated, as well as the hydrolysis of diaminopyrimidine to cytosine, isocytosine, and uracil. Thiourea also reacts with cyanoacetaldehyde to give 2-thiocytosine, but the pyrimidine yields are much lower than with guanidine hydrochloride or urea. Thiocytosine hydrolyzes to thiouracil and cytosine and then to uracil. This synthesis would have been a significant prebiotic source of 2-thiopyrimidines and 5-substituted derivatives of thiouracil, many of which occur in tRNA. The applicability of these results to the drying lagoon model of prebiotic synthesis was tested by dry-down experiments where dilute solutions of cyanoacetaldehyde, guanidine hydrochloride, and 0.5m NaCl were evaporated over varying periods of time. The yields of diaminopyrimidine varied from 1 to 7%. These results show that drying lagoons and beaches may have been major sites of prebiotic syntheses.