Effects of intervals between jumps or bouts on osteogenic response to loading.

Prolonged loading repetitions can diminish the mechanosensitivity of bones, and increased intervals between loading might restore sensitivity. This study was designed to investigate the effects of intervals between loadings or bouts on osteogenic response. Forty female Fisher 344 rats aged 5 wk were divided into a control group and three exercise groups: 20 jumps in a single bout with a 3-s (S3) or 30-s (S30) jump interval, or 20 jumps in 2 bouts (10 x 2) separated by a 6-h interval with a 3-s jump interval (D3). After 8 wk of training, the bone masses per body weight of the femur and tibia were significantly greater in the three exercise groups than in the control group, and these values were also greater in S30 than in S3, although they were at the same level in D3 and S3. These data suggest that a longer interval (30 s) between individual loading had more effective anabolic effects on bone than a shorter interval (3 s).     

Effects of Exogenous Amino Acids on Iron Uptake in Relation to their Effects on Photoperiodic Flowering in Lemna paucicostata 6746

The flowering of Lemna paucicostata 6746 grown on 14-h photoperiodwas enhanced by the addition of high concentrations of ironto the medium, which also increased the endogenous iron concentration.The addition of asparagine, aspartate, glutamate, -alanine,glycine or serine to the medium also increased the endogenousiron level, resulting in the promotion of flowering. In contrast,the addition of cysteine, cystine, glutamine, arginine, threonineor phenylalanine lowered the endogenous iron level, resultingin the inhibition of flowering. Glycine and asparagine added to the medium during an inductive96-h dark period did not promote iron uptake and had no effecton flowering, but when added during the subsequent 120-h lightperiod, they promoted both iron uptake and flowering response.The increase in the endogenous iron level seems to favor floraldevelopment rather than induction of photoperiodic floweringof Lemna paucicostata 6746. (Received September 8, 1986; Accepted March 31, 1987)     

Characterization of a novel acidic protein of 38 kDa, A0, in yeast ribosomes which immunologically cross-reacts with the 13 kDa acidic ribosomal proteins, A1/A2

A new ribosomal protein of 38 kDa, named A0, was detected in yeast ribosomes on immunoblotting. The antibody used here was that against A1/A2, 13 kDa acidic ribosomal proteins which cross-reacted with A0. Although A0 and A1/A2 share common antigenic determinants, they differ in the following biochemical properties. While A1/A2 could be extracted from ribosomes with ethanol and ammonium sulfate, A0 could not. A0 gave two protein spots in a less acidic region than for A1/A2 on two-dimensional gel electrophoresis. The heterogeneity observed for A0 was ascribable to phosphorylation because one spot disappeared after treatment of the ribosomes with phosphatase. The syntheses of A0 and A1/A2 are directed by different mRNA species, as judged with a cell-free translation system, ruling out the possibility that A0 is a precursor of A1/A2. Although a mammalian ribosomal protein equivalent to A0 has been shown to be associated with 13 kDa acidic proteins in the cytoplasm, essentially no A0 was detected on immunoblotting in the yeast cytosol, while a small but detectable amount of A1/A2 was present. The possibility that A0 is a eukaryotic equivalent of L10 of Escherichia coli is discussed.     

An NAD:cysteine ADP-ribosyltransferase is present in human erythrocytes

A novel enzymatic activity, i.e., the catalysis of the formation of ADP-ribosylcysteine, was found in the cytosol of human erythrocytes. The NAD:cysteine ADP-ribosyltransferase was partially purified by sequential chromatographic steps on phenyl-Sepharose, phosphocellulose, and Sepharose CL-6B. The enzyme has an apparent molecular weight of 27,000 +/- 3,000, as determined by gel permeation. The formation of ADP-ribosylcysteine was associated with the stoichiometric release of nicotinamide from NAD. The enzyme was found to be highly specific toward cysteine and cysteine methyl ester as ADP-ribose acceptors. S-Benzoyl-L-cysteine, cystine, histidine, glutamic acid, arginine, arginine methyl ester, and agmatine were ineffective as acceptors for this enzyme.     

The mechanism of action of ricin and related toxic lectins on eukaryotic ribosomes. The site and the characteristics of the modification in 28 S ribosomal RNA caused by the toxins

Ricin is a potent cytotoxic protein derived from the higher plant Ricinus communis that inactivates eukaryotic ribosomes. In this paper we have studied the mechanism of action of ricin A-chain on rat liver ribosomes in vitro. Our findings indicate that the toxin inactivates the ribosomes by modifying both or either of two nucleoside residues, G4323 and A4324, in 28 S rRNA. These nucleotides are located close to the alpha-sarcin cleavage site and become resistant to all ribonucleases tested. The examination of the lability of phosphodiester bonds of these nucleotides to both mild alkaline digestion and aniline treatment at acidic pH suggests that the base of A4324 is removed by the toxin. This unique activity of ricin A-chain was also observed when naked 28 S rRNA is used as a substrate, indicating that the toxin directly acts on the RNA. Similar activity on 28 S rRNA is also exhibited by abrin and modeccin, ricin-related toxins, suggesting a general mechanistic pathway for ribosome inactivation by lectin toxins.     

pH dependence of individual tryptophan N-1 hydrogen exchange rates in lysozyme and its chemically modified derivatives

Nuclear magnetic resonance analyses have been made of the individual hydrogen-deuterium exchange rates of tryptophan indole N-1 hydrogens in native lysozyme and its chemically modified derivatives including lysozyme with an ester cross-linkage between Glu-35 and Trp-108, lysozyme with an internal amide cross-linking between the epsilon-amino group of Lys-13 and the alpha-carboxyl group of Leu-129, and lysozyme with the beta-aspartyl sequence at Asp-101. The pH dependence curves of the exchange rates for Trp-63 and Trp-108 are different from those expected for tryptophan. The pH dependence curve for Trp-108 exchange exhibits the effects from molecular aggregation at pH above 5 and from a transition between the two conformational fluctuations at around pH 4. The exchange rates for tryptophan residues in native lysozyme and modified derivatives are not correlated with the thermodynamic or kinetic parameters in protein denaturation, suggesting that the fluctuations responsible for the exchange are not global ones. The exchange rates for tryptophan residues remote from the modification site are perturbed. Such tryptophan residues are found to be involved in a small but distinct conformational change due to the modification. Therefore, the perturbations of the N-1 hydrogen exchange rates are related to the minor change in local conformation or in conformational strain induced by the chemical modification.     

Infrageneric variation of the low molecular weight carbohydrate composition of the seeds of the genusVicia (Leguminosae)

The low molecular weight carbohydrate compositions of the seeds of 29 species ofVicia, namelyV. amoena, V. amurensis, V. bifolia, V. dumetorum, V. fauriei, V. japonica, V. nipponica, V. pisiformis, V. pseudo-orobus, V. sylvatica, V. unijuga, V. venosa, V. cassubica, V. orobus, V. cracca agg.,V. hirsuta, V. villosa agg.,V. tetrasperma,V. oroboides, V. sepium, V. cuspidata, V. grandiflora, V. lathyloides, V. sativa agg.,V. bithynica, V. faba, V. narbonensis, V. hybrida andV. lutea were determined by gas liquid chromatography. The carbohydrate compositions were found to be species-specific. Principal component analysis of the carbohydrate composition data showed that these species can be divided into three groups. Although, as far as the examined species were concerned, these groups were not correlated with the known subgenera, significant correlation between the groups and the known sections was detected in the subgenusVicia. The carbohydrate composition character would be important to clarify the relationships among closely related taxa of the genusVicia.     

Enhanced responsiveness to parathyroid hormone and induction of functional differentiation of cultured rabbit costal chondrocytes by a pulsed electromagnetic field

Pulsed electromagnetic fields promote healing of delayed united and ununited fractures by triggering a series of events in fibrocartilage. We examined the effects of a pulsed electromagnetic field (recurrent bursts, 15.4 Hz, of shorter pulses of an average of 2 gauss) on rabbit costal chondrocytes in culture. A pulsed electromagnetic field slightly reduced the intracellular cyclic adenosine 3',5'-monophosphate (cAMP) level in the culture. However, it significantly enhanced cAMP accumulation in response to parathyroid hormone (PTH) to 140% of that induced by PTH in its absence, while it did not affect cAMP accumulation in response to prostaglandin E1 or prostaglandin I2. The effect on cAMP accumulation in response to PTH became evident after exposure of the cultures to the pulsed electromagnetic field for 48 h, and was dependent upon the field strength. cAMP accumulation in response to PTH is followed by induction of ornithine decarboxylase, a good marker of differentiated chondrocytes, after PTH treatment for 4 h. Consistent with the enhanced cAMP accumulation, ornithine decarboxylase activity induced by PTH was also increased by the pulsed electromagnetic field to 170% of that in cells not exposed to a pulsed electromagnetic field. Furthermore, stimulation of glycosaminoglycan synthesis, a differentiated phenotype, in response to PTH was significantly enhanced by a pulsed electromagnetic field. Thus, a pulsed electromagnetic field enhanced a series of events in rabbit costal chondrocytes in response to PTH. These findings show that exposure of chondrocytes to a pulsed electromagnetic field resulted in functional differentiation of the cells.     

A new gene controlling the frequency of cell division per round of DNA replication in Escherichia coli

Summary A novel mutant of Escherichia coli, named cfcA1, was isolated from a temperature-sensitive dnaB42 strain, and found to have the following characteristics. Division arrest and lethality induced by inhibition of DNA replication was reduced and delayed in the cfcA1 dnaB42 strain, as compared with the parental dnaB42 strain. Two types of inhibition of division induced by the addition of nalidixic acid or hydroxyurea were suppressed by the cfcA1 mutation. Under permissive conditions for DNA replication, the colony forming ability of cfcA1 cells was significantly reduced as compared with that of cfc ⁺ cells; conversely the division rate of cfcA1 cells was higher than that of cfc ⁺ cells. The cfcA1 mutation partially restored division arrest induced in the thermosensitive ftsZ84 mutant at the restrictive temperature and suppresed the UV sensitivity of the lon mutation. The mutation was mapped at 79.2 min on the E. coli chromosome. Taking these properties into account, it is hypothesized that the cfcA gene is involved in determining the frequency of cell division per round of DNA replication by interacting with the FtsZ protein which is essential for cell division.