Peptidoglycan biosynthesis in stationary-phase cells of Escherichia coli.

The ability of stationary-phase cells of Escherichia coli W7 to incorporate radioactive precursors into macromolecular murein has been studied. During the initial 6 h of the stationary phase, resting cells incorporated meso-[3H]diaminopimelic acid at a rate corresponding to the insertion of 1.3 X 10(4) disaccharide units min-1 cell-1. Afterwards, the rate of incorporation dropped drastically (90%) to a low but still detectable level. Incorporation during stationary phase did not result in an increased amount of total murein in the culture, suggesting that it was related to a turnover process. Analysis of the effects of a number of beta-lactam antibiotics indicated that incorporation of murein precursors in stationary-phase cells was mediated by penicillin-binding proteins, suggesting that the activity of penicillin-binding protein 2 was particularly relevant to this process.     

Thyroid function and trisomy 21. TSH increase and rT3 deficiency

An excess of thyrotropin (TSH) with normal levels of tetraiodothyronine (T4) and of 3,5,3'-triiodothyronine (T3) was confirmed in the serum of 78 trisomy 21 children. A severe deficiency of 3,3',5'-triiodo-thyronine (rT3 or reverse T3) was observed and the decrease of the rT3/TSH ratio was highly significant. These new facts suggest that the rT3 deficiency plays a peculiar role in trisomy 21 (maybe through the regulation of one or few steps of monocarbons' metabolism). A systematic control of thyroid function (including the patient's rT3 level) is mandatory for the follow-up of every trisomy 21 patient.     

Isolation and Characterization of Methanogenic Bacteria from Landfills

Methanogenic bacteria were isolated from landfill sites in the United Kingdom. Strains of Methanobacterium formicicum, Methanosarcina barkeri, several different immunotypes of Methanobacterium bryantii, and a coccoid methanogen distinct from the reference immunotypes were identified.     

Studies on well-coupled Photosystem I-enriched subchloroplast vesicles — energy-dependent switching between two different active states of the proton-translocation adenosine triphosphatase

Single-turnover flash-induced ATP synthesis coupled to natural cyclic electron flow in Photosystem I-enriched subchloroplast vesicles (from spinach) was continuously followed by the luciferin-luciferase luminescence. The ATP yield per flash was maximal (1 ATP per s per 1000 Chl) around a flash frequency of 0.5–2 Hz. It decreased both at lower and higher flash frequencies. The decrease at high flash frequency was due to limitation by the electron-transfer rate, while the decrease at low flash frequency was directly due to intrinsic properties of the ATPase itself. Carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP) decreased the yield at low frequency more than at high frequency. The same behaviour was observed if electron transfer was artificially mediated by pyocyanin. If the ADP concentration was increased from 40 to at least 80 μM, or if the vesicles were preincubated with 5 mM dithiothreitol (DTT), the decrease of the yield at flash frequencies below 0.5 Hz was no longer observed. Incubation with DTT increased the rates of ATP hydrolysis and synthesis at any flash frequency. The decrease of the yield could be elicited again by addition of 50 nM FCCP. It is concluded that at low levels of the protonmotive force (Δ gm_H⁺), the ATPase is converted into an active ATP-hydrolyzing state in which ATP synthesis activity is decreased due to a decreased affinity towards ADP and/or to a decreased release of newly synthesized ATP, that can be cancelled by increasing the ADP concentration or by addition of DTT in the absence of uncoupler.     

Photoaffinity labeling of scorpion toxin receptors associated with insect synaptosomal Na+ channels

Photoreactive and radioiodinated derivatives of several scorpion toxins acting on insect Na+ channels were prepared without loss of their pharmacological activities. Photoaffinity experiments were carried out on a synaptosomal fraction from the nerve cord of the cockroach Periplaneta americana: with all toxin derivatives, a single specifically labeled band was obtained with a molecular weight of 188,000 +/- 12,000 (n = 17). These results indicate for the first time the molecular weight of the scorpion toxin receptor from the insect nervous system which is probably associated with voltage sensitive Na+ channels. One of these toxins, toxin VII from Tityus serrulatus venom, has been previously shown to be active both in mammals and in insects, in rat brain synaptosomes this toxin labeled a Mr = 31,000 +/- 4,000 band in contrast, to observations in the insect preparation.     

Periodic cleavage of poly(dA) by oligothymidylates covalently linked to the 1,10-phenanthroline-copper complex

1,10-Phenanthroline (OP) was covalently attached to the 3'-terminus of two oligothymidylates via different linkers [abbreviated as T8-(OP) and T6-(OP)]. In the presence of Cu2+ and 3-mercaptopropionic acid (MPA), these reagents induce a hybridization-dependent cleavage of poly(dA) and of a 27 nucleotide long oligodeoxynucleotide containing an A8 sequence. The principal cleavage sites on the 27-mer span four residues located near the 3'-terminal phosphate group of T8-(OP). When poly(dA) was degraded by T6-(OP) and T8-(OP), a series of bands were obtained corresponding to a repeat unit of six and eight nucleotides, respectively. This periodicity reflects the cooperative binding of oligothymidylate-OP to the polynucleotide matrix and the localized nicking sites.     

Biochemical and functional characterization of three types of coated vesicles in bovine adrenocortical cells: implication in the intracellular traffic

Three populations of pure coated vesicles from adrenocortical cells, differing in their density, i.e., 1.125-1.155, 1.155-1.175, and 1.175-1.210 g/cm3, are obtained after separation on two successive sucrose-2H2O gradients. They are involved in LDL internalization and in the receptor cycle as confirmed by the presence, in each population, of the LDL receptor. Electron micrographs confirm the existence of three homogeneous populations exhibiting the typical polygonal structure of the clathrin coat. They differ in their size distribution (small, congruent to 70-nm diameter; medium, congruent to 90-nm diameter; large, congruent to 110-nm diameter) and in the organization of clathrin and of the coat proteins as evidenced on electrophoreses carried out under nondenaturing and denaturing conditions. Activity measurements of marker enzymes, phosphodiesterase and galactosyltransferase, suggest that medium coated vesicles might originate from plasma membranes and small ones from the Golgi complex. Large coated vesicles exhibit phosphokinase enzyme and substrate polypeptides different from those of the two other populations, tubulins being the preferred kinase substrates for the small and medium coated vesicles. These kinases are autophosphorylating enzymes and are revealed, by nondenaturing electrophoreses, as different high molecular mass complexes in the three populations. Clathrin and coat proteins are not part of these complexes.     

Conditions for the formation of the oxo derivatives of arachidonic acid from platelet 12-lipoxygenase and soybean 15-lipoxygenase

Three carbonyl compounds derived from arachidonic acid have recently been characterized in human platelets, namely, 12-ketoeicosatetraenoic acid and two isomeric 12-oxododecatrienoic acids. The conditions for the synthesis of these compounds and for the synthesis of analogous products from soybean lipoxygenase, i.e., 15-ketoeicosatetraenoic acid and 15-oxopentadecatetraenoic acids, were compared with regard to the role of oxygen and fatty acid availability, and heme catalysis. Using platelet homogenates or soybean lipoxygenase and arachidonic acid as a substrate, it was found that the establishment of anaerobic conditions during the incubation was mandatory only for the synthesis of 15-oxopentadecatetraenoic acids. Anaerobic conditions, however, greatly increased the formation of 15-ketoeicosatetraenoic acid and, to a lesser extent, of 12-oxododecatrienoic acids. On the other hand, 12-hydroperoxyeicosatetraenoic acid (12-HPETE) was transformed into 12-ketoeicosatetraenoic acid and 12-oxododecatrienoic acids by platelet homogenates or soybean lipoxygenase. This transformation was increased when the incubation was performed in anaerobic conditions and in the presence of a fatty acid substrate of the enzyme. These data suggest that oxygen deprivation and excess fatty acid could play a stimulatory role in the synthesis of 12-oxo compounds by platelets. Finally, we have compared the heme-catalyzed generation of the 12-oxo and 15-oxo derivatives from their hydroperoxide precursors: whereas 12-oxododecatrienoic acids and 12-ketoeicosatetraenoic acid were formed in the proportion of 8.5: 1.5 from 12-HPETE incubated with hematin (150 nM), 15-ketoeicosatetraenoic acid was the only carbonyl compound generated from 15-HPETE in the same conditions, emphasizing the unique reactivity of the 12-HPETE.     

Sea urchin sperm head plasma membranes: characteristics and egg jelly induced Ca2+ and Na+ uptake

Sea urchin sperm respond to egg factors with changes in the ionic permeability of their plasma membrane. It has been previously shown that plasma membranes isolated preferentially from sea urchin sperm flagella respond to egg jelly increasing their Ca2+ and Na+ uptake (Darszon et al. (1984) Eur. J. Biochem. 144, 515-522). However, the egg jelly induced acrosome reaction occurs in the sperm head, and there is evidence for an heterogeneous distribution of plasma membrane components within the various regions of this cell. We here report a method for purifying sperm head membranes using positively charged beads according to Jacobson (1977) Biochim. Biophys. Acta 471, 331-335). Under the transmission electron microscope these membranes appeared homogeneous and apparently free of internal membranes. The yield of the preparation was 0.9% of the total protein in the sperm homogenate. The preparation contained less than 5% of the mitochondrial marker cytochrome oxidase, and 10% of the total DNA/mg protein. Surface labeling with 125I indicated a 2.5-3-fold enrichment in specific activity of the head membranes with respect to whole sperm. The SDS band pattern and the lipid composition of this preparation were different from those of isolated flagellar membranes. Phosphatidylcholine was higher in the head membranes, while phosphatidylserine and phosphatidylethanolamine were lower. The head membranes displayed a 1.7-2.3-fold higher Ca2+-ATPase activity and a 2.5-fold lower Na+/K+-ATPase activity, than the flagellar membranes. These results are consistent with a heterogeneous distribution of membrane components along the sea urchin sperm plasma membranes. Isolated head membranes sonicated in the presence of soybean phospholipid liposomes responded to egg jelly with a species-specific increase in Ca2+ and Na+ uptake. As in whole sperm, Ca2+ uptake was inhibited by the Ca2+ channel blocker nisoldipine. A close analog of this compound, [3H]nitrendipine, binds with high affinity to head membranes in a saturable, reversible manner, showing a Kd and Bmax of 31 nM and 5.3 pmol/mg protein, respectively.