Impact of predation by the robber fly Proctacanthus milbertii (Diptera: Asilidae) on grasshopper (Orthoptera: Acrididae) populations

The impact of predation by the robber fly Proctacanthus milbertii Macquart on populations of adult grasshoppers from grasslands of the Nebraska sandhills was estimated. Densities of P. milbertii were estimated at 437 individuals per hectare (2 se=122). Overall densities of 23 species of grasshoppers were estimated to be 64,000 individuals per hectare with the most abundant species (Ageneotettix deorum) having a population size of approximately 15,000 individuals per hectare. Based on three estimates of predation level (ranging from 0.5 to 2 prey per day per robber fly), P. milbertii may take from 0.5% to 2% of the adult grasshoppers per day. Species of grasshoppers were taken by P. milbertii in about the same proportion in which they occurred at the study site and no size-selective component of predation was detectable.     

Intracerebral injection of gamma vinyl GABA: Method for measuring rates of GABA synthesis in specific brain regions invivo

In order to obtain an index of the rate of GABA synthesis in different rat brain regions, we examined the rate of accumulation of GABA after irreversible inhibition of GABA-transaminase. Gamma-vinyl-GABA (GVG), a catalytic inhibitor of GABA-transaminase, was microinjected directly into each of four brain areas: superior colliculus (SC), substantia nigra (SN), frontal cortex (CTX) and caudate-putamen (CP). The subsequent rate of GABA accumulation was linear for at least 90 min in all regions, and was found to be 2–3 times higher in the SC and SN than in the CTX and CP. The nerve terminal contribution to the initial rate of GABA accumulation after GVG was determined by comparing values obtained in the intact SN with those obtained in the SN in which the GABAergic afferent terminals had been destroyed. The initial rate of GABA accumulation in the denervated SN was less than one-half of that measured in the intact SN, indicating that, under normal conditions, both nerve-terminal and non-nerve-terminal (perikarya, glia) compartments contribute to the rate of GABA accumulation after GABA-transaminase inhibition. Our results indicate that the intracerebral injection of GVG is a sensitive and reliable method for studying $\text{in}\text{vivo}$ GABA synthesis in brain. Although the rate of GABA accumulation after GVG is sensitive to changes in the nerve terminal compartment, other GABA compartments may also influence these measurements.     

Simultaneous inhibition of guinea pig brain 2′, 3′-cyclic nucleotide 3′-phosphohydrolase and myelin protein synthesis by 2′-adenosine monophosphate

Although the function of 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNPase) in myelin is unknown, the enzyme has been implicated in the metabolism of myelin proteins. Using 2′-AMP to inhibit CNPase, we examined the effect of reduced enzyme activity on the $\text{in vitro}$ incorporation of ¹⁴C-leucine into brain proteins. The results of this study revealed that (1) guinea pig brain homogenates incorporate leucine into protein from a sucrose medium in a linear fashion, (2) all brain fractions (cytosol, myelin, and microsomes) are labelled within 1 hr, (3) 2′-AMP inhibition of CNPase by 50% results in a similar inhibition of brain protein synthesis, and (4) the reduced protein synthesis is accompanied by a shift in label from myelin proteins to those found in the microsomes. These results are consistent with a role for CNPase in myelin protein synthesis.     

Effects of glucagon and insulin on liver lysosomes

Recent experimental evidence has been obtained, principally in the laboratory of Glenn Mortimore, that hepatic lysosomes can act as a pool of amino acids during fasting. This pool is generated through $\text{autophagy}$, whereby intracellular proteins are somehow captured by the lysosomes and then rapidly hydrolyzed to free amino acids by the lysosomal proteinases. Two important metabolic fates of these lysosomal digestive products can be: 1) conversion of the glucogenic amino acids into glucose, and 2) conversion of trimethyl-lysine into carnitine. The latter metabolite is required to transfer fatty acids to the mitochondrial site of β-oxidation. Most interesting is the observation that glucagon appears to induce lysosomal autophagy and the resulting degradation of intracellular proteins by decreasing the size of amino acid pools in the perfused liver. This effect of the hormone may be directed at the single amino acid glutamine, since adding it alone to the perfusate can prevent the increase in autophagy caused by glucagon. Insulin also rapidly inactivates hepatic autophagy and its ensuing proteolysis. The $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for the rate of los of autophagic vocuoles from the insulin-treated liver (or animal) is approximately 8 min. Thus, glucagon and insulin actively control intracellular protein catabolism that takes place within hepatic lysosomes, and this regulation by the two hormones may be one of their major molecular effects on gluconegenesis in the liver.     

The effect of copper on glutathione metabolism in human leukocytes

Leukocytes incubated with Cu(II) showed a decrease in both glutathione reductase activity and reduced glutathione content. The glucose 6-phosphate dehydrogenase activity under the same conditions was not affected. Serum albumin added to mixtures prevented the loss of enzyme activity, whiled-penicillamine andl-histidine had little effect. Prior oxidation of the cell-reduced glutathione did not diminish the enzyme inhibitory action of Cu(II). The amount of regeneration of reduced glutathione in leukocytes previously treated with diamide to oxidize their reduced glutathione was a function of Cu(II) concentration in the media. No evidence was obtained that elevated serum ceruloplasmin levels in rabbits, nor incubation of leukocytes in vitro with ceruloplasmin, affect leukocyte glutathione reductase activity. It was proposed that the major mechanism by which copper affects glutathione metabolism in leukocytes is by inhibition of glutathione reductase.     

Properties of a novel ATPase enzyme in chromaffin granules

Membranes were isolated from mitochondria and chromaffin granules of bovine adrenal medullae. The cross-contamination between the two membranes was examined by comparing the radioactive bands on autoradiograms of gels after phosphorylation of the membranes with [-³²P]-ATP and decoration with [¹²⁵I]concanavalin A and [¹²⁵I]protein A with antibody that was raised against chromaffin-granule membranes. It was found that the membranes cross-contaminated each other by less than 10%. The technique of immunodecoration with antibodies against subunits of proton-ATPases from yeast mitochondria, spinach chloroplasts, andE. coli membranes was used for quantitative estimation of proton-ATPase complexes in chromaffin granules and mitochondrial membranes. It was found that chromaffin-granule membranes contain less than 10% of the amount of proton-ATPase complex in mitochondrial membranes. The specific ATPase activity of chromaffin-granule membranes was on the order of 30 to 50% of the mitochondrial membranes. The ATPase activity of the chromaffin-granule membranes was more sensitive to 4-acetamido-4-isothiocyano-2,2-disulfonic acid stilbene and 4-chloro-7-nitrobenzofurazan. It was much less sensitive than the mitochondrial membranes to antibody against subunit of proton-ATPase fromE. coli membranes. After solubilization of chromaffin-granule membranes by octyglucoside and cholate and subsequent centrifugation on sucrose gradient, two different ATPase enzymes were separated. The heavier enzyme was identical to the mitochondrial-ATPase complex, while the lighter enzyme was identified as a novel ATPase, which might be responsible for the special properties of the ATPase activity of chromaffin-granule membranes.Abbreviations DCCD dicyclohoxylcarbodiimide - NBD-Cl 4-chloro-7-nitrobenzofurazan - SITS 4-acetamido-4-isothiocyano-2,2-disulfonic acid stilbene - SDS sodium dodecyl sulfate - MES 2-(N-morpholino)ethane sulfonic acid - FITC fluorescein isothiocyanate     

Guanosine-5′-diphosphate-3′-diphosphate inhibits the in, vitro synthesis of β-lactamase from pBR322 DNA

The $\text{in}\text{,}\text{vitro}$ synthesis of β-lactamase directed by pBR322 DNA is inhibited by guanosine-5′-diphosphate-3′-diphosphate.     

Lysosomal pool of free-amino acids

Free (non-protein) amino acids were measured in whole rat liver and in unmodified lysosomes which were prepared from rat liver by the technique of free-flow electrophoresis. Significant intralysosomal pools of threonine, serine, valine, cystine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine and arginine were found. No efflux occurred from rat liver lysosomes in isotonic buffered sucrose at 0°C, but all amino acids showed various degrees of efflux at 20⁰ and 37⁰.     

Monitoring river periphyton with artificial benthic substrates

The objective of this research was to identify the materials and methods necessary to study the attached algal community on a river bottom in deep water. The study site was the Susquehanna River near Falls, Pennsylvania. Artificial substrates of smooth glass, frosted glass, Vermont slate, sandy slate (flagstone) and acrylic plate were placed on the stream bottom in detritus free sample holders by scuba divers. Both monthly and long-term cumulative samples were collected from the plates employing scuba and a Bar-Clamp sampler. River stones (natural substrates) were collected for comparison. Samples were analyzed in a Palmer Cell under a Bausch and Lomb research microscope. Diatoms were the most important colonizers of river stones, with the genera Nitzschia and Navicula most abundant. Highest periphyton densities occurred on natural substrates in winter with a maximum of 2.2 × 10⁴ units/ mm². Artificial substrates with one month exposure periods accumulated maximum periphyton density from May through October with relatively low densities in winter. Cumulative artificial substrates were most like river stones in patterns of colonization. Frosted acrylic is recommended for future studies employing benthic artificial periphyton substrates.This study was partially supported by the Pennsylvania Power and Light Company