The energy utilized in protein breakdown by the ATP-dependent protease (La) from Escherichia coli

A crucial enzyme in the pathway for protein degradation in Escherichia coli is protease La, an ATP-hydrolyzing protease encoded by the lon gene. This enzyme degrades various proteins to small polypeptides containing 10-20 amino acid residues. To learn more about its energy requirement, we determined the number of ATP molecules hydrolyzed by the purified protease for each peptide bond cleaved. The enzyme hydrolyzed about 2 molecules of ATP for each new amino group generated with casein, bovine serum albumin, glucagon, or guanidinated casein as substrates, even though these proteins differ up to 20-fold in size and 3-4 fold in rates of hydrolysis of peptide bonds. Similar values for the stoichiometry (from 1.9 to 2.4) were obtained using fluorescamine or 2,4,6-trinitrobenzene sulfonic acid to estimate the appearance of new amino groups. These values appeared lower at 1 mM than at 10 mM Mg2+. The coupling between ATP and peptide bond hydrolysis appeared very tight. However, when the protease was assayed under suboptimal conditions (e.g. at lower pH or with ADP present), many more ATP molecules (from 3.5 to 12) were consumed per peptide bond cleaved. Our data would indicate that the early steps in protein degradation consume almost as much energy (2 ATPs for each cleavage) as does the formation of peptide bonds during protein synthesis.     

The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: II. Na+−Cl− symport is independent of K+

Summary In the epithelium of rabbit gallbladder, in the nominal absence of bicarbonate, intracellular Cl^– activity is about 25mm, about 4 times higher than intracellular Cl^– activity at the electrochemical equilibrium. It is essentially not affected by 10^–4 m acetazolamide and 10^–4 m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS) even during prolonged exposures; it falls to the equilibrium value by removal of Na⁺ from the lumen without significant changes of the apical membrane potential difference. Both intracellular Cl^– and Na⁺ activities are decreased by luminal treatment with 25mm SCN^–; the initial rates of change are not significantly different. In addition, the initial rates of change of intracellular Cl^– activity are not significantly different upon Na⁺ or Cl^– entry block by the appropriate reduction of the concentration of either ion in the luminal solution. Luminal K⁺ removal or 10^–5 m bumetanide do not affect intracellular Cl^– and Na⁺ activities or Cl^– influx through the apical membrane. It is concluded that in the absence of bicarbonate NaCl entry is entirely due to a Na⁺–Cl^– symport on a single carrier which, at least under the conditions tested, does not cotransport K⁺.     

The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: I. Na+/H+, Cl−/HCO 3 − double exchange and Na+−Cl− symport

Summary Cl^– influx at the luminal border of the epithelium of rabbit gallbladder was measured by 45-sec exposures to³⁶Cl^– and³H-sucrose (as extracellular marker). Its paracellular component was evaluated by the use of 25mm SCN^– which immediately and completely inhibits Cl^– entry into the cell. Cellular influx was equal to 16.7eq cm^–2 hr^–1 and decreased to 8.5eq cm^–2 hr^–1 upon removal of HCO ₃ ^– from the bathing media and by bubbling 100% O₂ for 45 min. When HCO ₃ ^– was present, cellular influx was again about halved by the action of 10^–4 m acetazolamide, 10^–5 to 10^–4 m furosemide, 10^–5 to 10^–4 m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS), 10^–3 m amiloride. The effects of furosemide and SITS were tested at different concentrations of the inhibitor and with different exposure times: they were maximal at the concentrations reported above and nonadditive. In turn, the effects of amiloride and SITS were not additive. Acetazolamide reached its maximal action after an exposure of about 2 min. When exogenous HCO ₃ ^– was absent, the residual cellular influx was insensitive to acetazolamide, furosemide and SITS. When exogenous HCO ₃ ^– was present in the salines, Na⁺ removal from the mucosal side caused a slow decline of cellular Cl^– influx; conversely, it immediately abolished cellular Cl^– influx in the absence of HCO ₃ ^– . In conclusion, about 50% of cellular influx is sensitive to HCO ₃ ^– , inhibitable by SCN^–, acetazolamide, furosemide, SITS and amiloride and furthermore slowly dependent on Na⁺. The residual cellular influx is insensitive to bicarbonate, inhibitable by SCN^–, resistant to acetazolamide, furosemide, SITS and amiloride, and immediately dependent on Na⁺. Thus, about 50% of apical membrane NaCl influx appears to result from a Na⁺/H⁺ and Cl^–/HCO ₃ ^– exchange, whereas the residual influx seems to be due to Na⁺–Cl^– contranport on a single carrier. Whether both components are simultaneously present or the latter represents a cellular homeostatic counterreaction to the inhibition of the former is not clear.     

Subcellular Location and Neuronal Release of Diazepam Binding Inhibitor

Diazepam binding inhibitor (DBI), a peptide located in CNS neurons, blocks the binding of benzodiazepines and beta-carbolines to the allosteric modulatory sites of gamma-aminobutyric acid (GABAA) receptors. Subcellular fractionation studies of rat brain indicate that DBI is compartmentalized. DBI-like immunoreactivity is highly enriched in synaptosomes obtained by differential centrifugation in isotonic sucrose followed by a Percoll gradient. In synaptosomal lysate, DBI-like immunoreactivity is primarily associated with synaptic vesicles partially purified by differential centrifugation and continuous sucrose gradient. Depolarization induced by high K+ levels (50 mM) or veratridine (50 microM) released DBI stored in neurons of superfused slices of hypothalamus, hippocampus, striatum, and cerebral cortex. The high K+ level-induced release is Ca2+ dependent, and the release induced by veratridine is blocked by 1.7 microM tetrodotoxin. Depolarization released GABA and Met5-enkephalin-Arg6-Phe7 together with DBI. DBI is also released by veratridine depolarization, in a tetrodotoxin-sensitive fashion, from primary cultures of cerebral cortical neurons, but not from cortical astrocytes. Depolarization fails to release DBI from slices of liver and other peripheral organs. These data support the view that DBI may be released as a putative neuromodulatory substance from rat brain neurons.     

Developmental and Dimensional Changes in the Cambial Fusiform Initials ofHoloptelea integrifolia (Roxb.) Planch.

Divisional activity, intrusive growth of the cell wall and loss of fusiform initials have been studied in Holoptelea integrifolia. The dimensional changes in relation to mean length, length frequency, mean width and length variation in relation to fibre length have also been analysed.     

Synthesis of rhodanese in Hep 3B cells

Summary The biosynthesis of rhodanese was studied in human hepatoma cell lines by immunoblotting and pulselabeling experiments using polyclonal antibodies raised against the bovine liver enzyme. Rhodanese, partially purified from human liver, showed an apparent molecular weight of 33,000 daltons, coincident with that of rhodanese from Hep 3B cells. After pulse labeling of Hep 3B cells both at 37°C and 25°C, rhodanese in the cytosol fraction exhibited the same molecular weight as the enzyme isolated from the particulate fraction containing mitochondria. Moreover, newly synthesized rhodanese from total Hep 3B RNA translation products showed the same electrophoretic mobility as rhodanese from Hep 3B cells. These results suggest that rhodanese, unlike most mitochondrial proteins, is not synthesized as a higher molecular weight precursor.     

A genetic linkage map of chromosome 17

We have developed a genetic linkage map of 19 markers (including nine genes) on human chromosome 17, providing 13 reference points along virtually the entire length of this chromosome. The map covers an estimated 149 cM in length (sex-averaged), with a total length of 214 cM in females and 95 cM in males. This sex difference appears to be significant along virtually the entire length of the map. This map will be useful both for providing reference points for fine structure genetic and physical mapping and for genetic linkage studies of diseases, including von Recklinghausen neurofibromatosis and Charcot-Marie-Tooth disease.     

Accumulation and Interconversion of Amino Acids in Rice Roots under Anoxia

In excised rice roots, anaerobic degradation of proteins gaverise to an increase of free-amino acids. Anoxic accumulationof alanine, -aminobutyric acid and proline was the consequenceof the interconversion of glutamate, aspartate and amides. Theshift in the composition of the amino acid pool appears to becaused by changes in keto acid levels. The role of reactionsinvolved in amino acid interconversion and the physiologicalsignificance of these interconversions are considered and discussed. (Received November 25, 1988; Accepted June 9, 1988)     

Effects of membrane potential on Na cotransports in eel intestinal brush-border membrane vesicles: Studies with a fluorescent dye

Summary The Na-dependent transport of a number of organic molecules (d-glucose,l-proline,l-alanine,l-phenylalanine) in brush-border membrane vesicles isolated from the intestine of the eel (Anguilla anguilla) was monitored by recording the fluorescence quenching of the voltage-sensitive cyanine dye 3,3-diethylthiacarbocyanine iodide (DiS-C₂(5)). The experimental approach consisted of: a) generating an inside-negative membrane potential mimicking in vivo conditions: b) measuring the rate of membrane potential decay (i.e., the rate of fluorescence quenching decay) due to Na-neutral substrate cotransport. Rates of membrane potential decay showed saturation on substrate concentration andK _app values (the substrate concentration giving 50% of the maximal rate) were estimated for Na-dependent transport ofd-glucose (0,099mm),l-alanine (0.516mm),l-proline (0.118mm) andl-phenylalanine (2.04mm). The influence of an inside-negative membrane potential on the affinity of the transporter for glucose and for sodium is discussed.