Electron microscopic demonstration of rat liver glycogen phosphorylase activity with iron (Fe++)

Summary In this study a new electron microscopic method for the demonstration of liver glycogen phosphorylase activity has been presented.Prior to incubation the liver samples were shortly fixed in cold paraformaldehyde. Inorganic phosphate, liberated in the reaction catalyzed by the enzyme, were precipitated with iron (Fe⁺⁺) present in the incubating medium. Postfixation was performed in glutaraldehyde and osmium tetroxide.The ferrous phosphate precipitate was detected electron microscopically in unstained sections.The precipitate was mainly localized to endoplasmic membranes but also in glycogen particles. The method is imperfect in demonstrating phosphorylase activity bound to glycogen particles because of poor preservation of glycogen during treatment.     

Degradation of polysaccharides containing uronic acid residues

A method for the selective degradation of polysaccharides containing uronic acid residues is described. It involves methylation of hydroxyl and carboxyl groups, base-catalysed elimination, and mild hydrolysis with acid. The degraded product is etherified with trideuteriomethyl or ethyl groups and hydrolysed, and the resulting mixture of etherified sugars is analysed, as the alditol acetates, by g.l.c.—m.s. Comparison of this analysis with the methylation analysis of the original polysaccharide gives information on the nature of the sugar residues on either side of the uronic acid residue.     

Differential cytotoxicity of activated lymphocytes on allogeneic and xenogeneic target cells. II. Activation by phytohemagglutinin

In the preceding paper it has been shown that human or mouse lymphocytes stimulated by a variety of agents, damaged allogeneic target cells while damage of xenogeneic target cells was weak or absent. In this study, the species specificity of the cytotoxicity of PHA activated lymphocytes has been studied in greater detail. Effector cells were purified lymphocytes either from human peripheral blood, or from spleen or lymph nodes of inbred mice. Target cells were ⁵¹Cr-labeled human Chang liver cells or mouse L cells.PHA stimulated human or mouse lymphocytes were significantly more cytotoxic to allogeneic than to xenogeneic target cells. At low PHA doses at which damage of allogeneic target cells was significant, damage of xenogeneic target cells was very weak or absent. At higher PHA doses, damage of xenogeneic target cells became also significant but always remained at a lower level than that of allogeneic target cells.Prestimulation of human lymphocytes with PHA for 3 days increased their cytotoxic efficiency. Furthermore, damage of human Chang cells by human lymphocytes had a dose-response relationship similar to that valid for stimulation of DNA synthesis. However, damage of mouse L cells by human lymphocytes increased at PHA-doses at which stimulation of DNA-synthesis declined. For mouse lymphocytes, these doseresponse relationships were less clear-cut, probably due to differences in origin and survival of the effector cells. This confirms previous observations that cytotoxicity and DNA-synthesis are different but probably interdependent expressions of lymphocyte activation.     

Metabolic Regulation by Homoserine in Escherichia coli B/r

A mathematical analysis of branched pathway regulation has led to the prediction of a novel homoserine control in Escherichia coli B. Experimental support for such control is presented in this paper. Homoserine, the precursor of both threonine and methionine, inhibits nicotinamide adenine dinucleotide phosphate (NADP(+))-specific glutamate dehydrogenase (EC 1.4.1.4), the enzyme catalyzing the first reaction in ammonia assimilation. Physiological and biochemical evidence for this effect are offered. Homoserine depresses the growth rate of the organism, and glutamate, the product of the inhibited reaction, reverses this effect. The NADP(+)-specific glutamate dehydrogenase activity in cell-free extracts is inhibited by homoserine, and this inhibition parallels the restriction of growth rate. These effects are found in other enteric bacteria which share a similar overall pattern of control for the amino acids derived from aspartate. On the other hand, a sampling of more distantly related species which have different pathways and/or regulatory patterns provides no evidence for homoserine inhibition of the glutamate dehydrogenase reaction.     

The Fertility of Melanesian Girls, Laboratory Mice, and Prostitutes: A Comment on the "Bruce Effect"

Greenfield has recently proposed that low fertility in both prostitutes and unmarried Trobriand girls may be explained by the "Bruce effect": the inhibition of pregnancy in female mice that have had intercourse with different males within a short period. An examination of Malinowski's data indicates that a Trobriand girl usually had intercourse with only one man over a fairly long period and her sex life was not at all comparable to that of a prostitute or one of Bruce's mice. Low fertility in unmarried girls has been well documented for several Melanesian societies that differ notably in the behavior permitted to girls. The existence of so-called adolescent sterility still seems to be the best explanation to cover all of these cases. [fertility, sexual behavior, Melanesia]     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.     

Modified Microbiological Assay for Rapid Estimation of Antibiotic Concentrations in Human Sera

Antibiotic concentrations in human sera were estimated in 5 to 6 hr by a modified microbiological assay. By using Staphylococcus aureus and Streptococcus pyogenes as the assay organisms, the seeded assay plates were preincubated for 2 to 6 hr and then were stored at 4 C until used for assay. Paper discs saturated with the specimen were placed on the preincubated assay plates with reference discs saturated with known concentrations of antibiotic. After 5 to 6 hr of incubation, zones of antibacterial activity were measured and compared with a standard curve for estimation of antibiotic concentration. Results from this rapid assay method compared favorably with those from the commonly used 24-hr assay.