Cloning and sequencing of the metallothioprotein beta-lactamase II gene of Bacillus cereus 569/H in Escherichia coli

The structural gene for beta-lactamase II (EC 3.5.2.6), a metallothioenzyme, from Bacillus cereus 569/H (constitutive for high production of the enzyme) was cloned in Escherichia coli, and the nucleotide sequence was determined. This is the first class B beta-lactamase whose primary structure has been reported. The amino acid sequence of the exoenzyme form, deduced from the DNA, indicates that beta-lactamase II, like other secreted proteins, is synthesized as a precursor with a 30-amino acid N-terminal signal peptide. The pre-beta-lactamase II (Mr, 28,060) is processed in E. coli and in B. cereus to a single mature protein (Mr, 24,932) which is totally secreted by B. cereus but in E. coli remains intracellular, probably in the periplasm. The expression of the gene in E. coli RR1 on the multicopy plasmid pRWHO12 was comparable to that in B. cereus, where it is presumably present as a single copy. The three histidine residues that are involved (along with the sole cysteine of the mature protein) in Zn(II) binding and hence in enzymatic activity against beta-lactams were identified. These findings will help to define the secondary structure, mechanism of action, and evolutionary lineage of B. cereus beta-lactamase II and other class B beta-lactamases.     

Abridged life tables for Pakistan based on the 1971 Population Growth Survey

A new set of abridged life tables for Pakistan is presented. Data from the 1971 Population Growth Survey were 1st analyzed to estimate the degree of completeness of the reporting of male and female deaths; female deaths were substantially more underreported than male deaths. Age-sex specific mortality schedules were adjusted accordingly. Life expectancy was around 50 years at birth, but increased by 8-9 years for those surviving the substantial risks of dying in the 1st year of life. No significant sex differential in mortality could be discerned from the life tables. The present life tables exhibit mortality levels which are very similar to those observed in the life tables based on the 1962-64 Population Growth Estimation data. The only exception in the present life tables is the lack of a significant improvement in female mortality beyond the reproductive ages possibly because the extent of underreporting of femal deaths found in the 1971 Population Growth Survey was substantially higher than that for males.     

A note on auxotrophic mutants of cowpea rhizobia

We have examined a variety of common mutagens in producing auxotrophic mutants in cowpea rhizobia strains JRC23 and IRC256. While NTG (N-methyl-N-nitro-N-nitrosoguanidine), EMS (ethylmethane sulfonate), NA (nitrous acid), and UV (ultraviolet) irradiation were mutagenic with the strain JRC23, these mutagenic agents did not mutate strain IRC256. On the contrary, transposon mutagenesis with Tn5 yielded auxotrophs in strain IRC256 but not in strain JRC23, while only methionine (Met^–) auxotrophs from strain JRC23, histidine (His^–), and adenine plus thiamine (Ade^–+Thi^–) auxotrophs from strain IRC256 were isolated.     

Effects of separate rib cage and abdominal restriction on exercise performance in normal humans

We assessed the effects of selective restriction of movements of the rib cage (Res,rc) and abdomen (Res,ab) on ventilatory pattern, transdiaphragmatic pressure (Pdi), and electrical activity of the diaphragm (Edi) in five normal subjects exercising at a constant work rate (80% of maximum power output) on a cycle ergometer till exhaustion. Restriction of movements was achieved by an inelastic corset applied tightly around the rib cage or abdomen. Edi was recorded by an esophageal electrode, rectified, and then integrated, and peak values during inspiration were measured. Each subject exercised at the same work rate on 3 days: with Res,rc, with Res,ab, and without restriction (control). Res,rc but not Res,ab reduced exercise time (tlim). Up to tlim, minute ventilation (VE) was similar in all three conditions. At any level of VE, however, Res,rc decreased tidal volume and inspiratory and expiratory time, whereas Res,ab had no effect on the pattern of breathing. Res,ab was associated with higher inspiratory Pdi swings at any level of VE, whereas peak Edi was similar to control. Inspiratory Pdi swings were the same with Res,rc as control, but the peak Edi for a given Pdi was greater with Res,rc (P less than 0.05). During Res,rc the abdominal pressure swings in expiration were greater than with Res,ab and control. We conclude that Res,rc altered the pattern of breathing in normal subjects in high-intensity exercise, decreased diaphragmatic contractility, increased abdominal muscle recruitment in expiration, and reduced tlim. On the other hand, Res,ab had no effect on breathing pattern or tlim but was associated with increased diaphragmatic contractility.     

Selection of thermotolerant yeast strains for biomass production from sudanese molasses

Summary Yeast isolates were obtained from different stages in the sugar refining process in an attempt to isolate thermotolerant strains which would grow on a molasses urea medium. Several strains which gave biomass yields of 30–41% at 40° were isolated and identified. Four of these strains were shown to be more resistant to a 15 minute incubation at 55° than three mesophilic strains.     

Receptors on phaeochromocytoma cells for two members of the PP-fold family--NPY and PP

Pancreatic polypeptide (PP) and neuropeptide Y (NPY) belong to a family of regulatory peptides which hold a distinct tertiary structure, the PP-fold, even in dilute aqueous solution. High-affinity receptors, specific for both PP and NPY, are described on the rat phaeochromocytoma cell line, PC-12. The binding of [125I-Tyr36]PP to PC-12 cells was inhibited by concentrations of unlabeled PP which correspond to physiological concentrations of the hormone, 10(-11)-10(-9) mol/l. The affinity of the receptor for the neuropeptide, NPY, was 10(2)-times lower than that of the PP receptor. C-terminal fragments of both PP (PP24-36) and NPY (NPY13-36) were between 10(2)- and 10(3)-times less potent in displacing the radiolabeled 36-amino-acid peptides from their respective receptors. It is concluded that PC-12 cells are suited for structure-function studies of the PP-fold peptides and studies on the cellular events following cellular binding of PP-fold peptides.     

Biotransformation of 7, 12-dimethylbenz (a) anthracene(DMBA): On the genesis of DMBA-trans-dihydrodiols and DMBA- 7- and 12-methyl hydroxylated metabolites

Biotransformation of DMBA in various induced and uninduced S-10 fractions in the presence and absence of hepatic mixed function oxidase inhibitors (α-naphthoflavone, metyrapone, SKF-525A and CS₂) is described. Particular attention is paid to the production of dihydrodiols (DHD) and DMBA-7-and 12-methyl hydroxylated metabolites. It is suggested that DMBA-3, 4-DHD, 8,9-DHD and 5, 6-DHD formation and DMBA-7-and 12-methyl hydroxylations proceed predominantly via different enzyme systems.     

Immunomodulatory effects of cholera toxin in mice

Immunomodulatory effects of cholera toxin (CT) were investigated in a murine model using various immunological parameters. C3H/HeN mice were injected with 2 micrograms of CT at various intervals (from 6 h to 21 days) before the immunological assays. Thymocytes were markedly decreased in their absolute number, and the phenotypes in such cells were clearly shifted from Thy1.2high+ PNAhigh+ to Thy1.2low+ PNAlow+ 2-4 days after the CT treatment. Spleen T cells were relatively increased, while surface IgM positive B cells were rather decreased. Natural killer activity and in vivo and in vitro cytotoxic T lymphocyte activity were markedly suppressed during the early stages after the CT treatment but recovered completely within 21 days. Mixed lymphocyte reaction was profoundly suppressed at least for the 1st week after the CT treatment. Furthermore, EL-4 tumor of C57BL/6 origin grew progressively and killed the recipient C3H mice when such tumor cells were inoculated 6 h after the CT treatment. On the contrary, a marked augmentation of direct (IgM) and indirect (IgG) plaque-forming cell responses to sheep red blood cells was seen after CT treatment. Delayed footpad reaction to SRBC was also augmented after CT treatment. As the mechanisms, both direct augmentation of CD4+ T cells and direct suppression of CD8+ T cells appeared to occur at a time due to the CT treatment. An indirect effect of CT through the release of the endogenous steroids was dismissed in the present study. Taken together, CT appears to have differential immunomodulatory effects on various immune effector cells through various mechanisms.