Physical properties of rod-shaped molecules in solution

Several theories describing the physical properties of solutions containing rod-shaped molecules are reviewed. The results of the various theories are presented in a convenient form for implementation on a calculator or microcomputer. Expressions are derived for light scattering from thin rods using rational approximations for the sine and cosine integrals. These expressions apply to turbidity, Rayleigh, and dynamic light-scattering measurements. Accurate approximating equations are given for the various diffusional motions involved in dynamic light scattering. For shear-dependent viscosity and flow birefringence, empirically derived interpolation formulas are given. These provide values of the Simha factor, extinction angle and orientation function for a wide range of axial ratios and velocity gradients with relative errors less than 1%. We demonstrate how these equations can be applied to predict or model the properties of a solution containing thin rods of various lengths.     

Design of a system for the control of low dissolved oxygen concentrations: critical oxygen concentrations for Azotobacter vinelandii and Escherichia coli

The physiological activity of microorganisms in environments with low dissolved oxygen concentrations often differs from the metabolic activity of the same cells growing under fully aerobic or anaerobic conditions. This article describes a laboratory-scale system for the control of dissolved oxygen at low levels while maintaining other parameters, such as agitator speed, gas flowrate, position of sparger outlet, and temperature at fixed values. Thus, it is possible to attribute in dilute nonviscous fermentations all physiologic changes solely to changes in dissolved oxygen. Experiments were conducted with Azotobacter vinelandii and Escherichia coli. Critical oxygen concentrations for growth (that value of oxygen allowing growth at 97% of mu max) were measured as 0.35 +/- 0.03 mg/L for A. vinelandii and 0.12 +/- 0.03 mg/L for E. coli. These values are significantly different from the commonly quoted values for critical oxygen concentrations based on respiration rates. Because of the superior dissolved oxygen control system and an improved experimental protocol preventing CO2 limitation, we believe that the values reported in this work more closely represent reality.     

beta-Glucosidase of Penicillium funiculosum. I. Purification

A strain of Penicillium funiculosum, isolated in this laboratory, produced in high yield both endo- and exo-glucanases and beta-glucosidases, which were suitable for the saccharification of cellulosic materials. The isolation of the beta-glucosidase of this organism, which differs from other beta-glucosidases of fungi in its substrate specificity, by preparative electrophoresis, is described in this article. The organism was grown on a lactose-casein medium and the culture filtrate concentrated by ammonium sulfate precipitation and dialysis. Electrophoresis was carried out on large slabs of polyacrylamide gel in an anodicrun in the presence of borate at pH 7. After elution of active fractions, a cathodic run was made at pH 6.0. Two precipitations with ammonium sulfate resulted in a homogeneous enzyme (specific activity 174 IU/mg). A second isozyme was also produced by P. funiculosum on cellulose-wheat bran medium. This isozyme was purified by electrophoresis at pH 7.0 in the absence of borate and was obtained free from other isozymes of beta-glucosidase and cellulases.     

Solid-state conformation of some basic sequential polypeptides

We have studied the structure of solid films obtained by x-ray diffraction, from several basic polypeptides with a defined sequence. The alterating polypeptides poly(Ala-Lys), poly(Leu-Lys), poly(Val-Lys), and poly(Arg-Leu) all show a cross-β-structure in which layers of hydrophilic side chains alternate with layers containing hydrophobic side chains. The other polypeptides studied are not in the β-conformation and appear to be in the α-helical conformation. The helices obtained from poly(Lys-Ala-Ala) and poly(Lys-Ala-Ala-Lys) appear to be packed in an unusual fashion, which favors interaction between alanine side chains. Such behavior is not found in poly(Lys-Leu-Ala).     

Invertase activity of intact cells of Saccharomyces cerevisiae growing on sugar cane molasses. I. Steady-state continuous culture tests

During the steady-state continuous culture of Saccharomyces cerevisiae on sugar cane blackstrap molasses under different experimental conditions, oscillatory variations of the invertase activity of the intact yeast cells were observed. The continuous morphological changes of the cells wall and of the periplasmic space affecting the interaction between invertase and sucrose molecules could be responsible by the observed oscillatory phenomena. The average invertase activity at the steady state is linearly correlated to the cell's growth rate.     

Some extensions of a linear model for categorical variables

The Grizzle-Starmer-Koch (GSK) model is extended to include the traditional log-linear model and a general class of Poisson and conditional Poisson distributions. Estimators of the model parameters are defined under general exact and stochastic linear constraints.     

A two-sample test sensitive to crossing hazards in uncensored and singly censored data

Savage score statistics are employed to develop a test for comparing survival distributions with right-hand singly censored data. The procedure is motivated by the interest in developing a powerful method for determining differences when true survival distributions cross. Examination of small-sample characteristics under the null hypothesis indicate that asymptotic critical values yield a slightly conservative test. Power of the test compares favorably with other criteria, including the modified Smirnov procedure, particularly if there is a single crossing of the survival curves.     

Evidence for a role of prostaglandin I2 and thromboxane A2 in the ductus venosus of the lamb

The prostaglandin (PG) endoperoxide, PGH2, and the thromboxane (TX) A2 analog, 9,11-epithio-11,12-methano-TXA2, were tested in vitro on the ductus venosus sphincter from fetal (premature and mature) and neonatal (1-day-old) lambs. PGH2 relaxed the indomethacin-contracted fetal ductus in a dose-dependent manner and its action was reduced after treatment with 15-hydroperoxyarachidonic acid. In contrast, reduced glutathione did not affect the PGH2 relaxation in the indomethacin-treated ductus, nor did it modify the response of the untreated ductus to constrictor stimuli. Unlike PGH2, the stable 9 alpha,11 alpha-epoxymethano-PGH2 analog contracted the vessel. Similarly, the TXA2 analog was a contractile agent, its action exceeding that of the PGH2 analog in potency and efficacy. The TXA2 analog was active on preparations from both premature (minimum 117 days gestation) and mature lambs, but a maximal effect was attained during the perinatal period. These results confirm the existence of a PG-mediated relaxing mechanism in the ductus venosus and suggest that the active compound is PGI2. This mechanism is likely responsible for keeping the ductus patent in the fetus. TXA2, formed within the liver parenchyma, is well suited for playing a role in postnatal closure of the vessel.     

Characterization of corticosteroid receptors in natural killer cells: comparison with circulating lymphoid and myeloid cells

Lymphocytes mediating natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) activities are relatively refractory to the changes in circulatory traffic and intrinsic function induced in other cell types by in vivo and in vitro corticosteroids (CS). To investigate if such drug resistance could be attributed to differences in the CS receptor number of affinity (Kd) of these cells, these characteristics were determined in purified populations of large granular lymphocytes (LGL), monocytes, neutrophils (PMN), and T cells. All cell types displayed a single class of CS receptor of uniform affinity; however, LGL resembled monocytes and PMN in receptor number and Kd while T cells had significantly fewer sites per cell with lower Kd. These studies suggest that the unresponsiveness of NK activity to CS is not secondary to differences in CS receptor capacity or affinity.     

Islet activating protein inhibits physiological responses evoked by cardiac muscarinic acetylcholine receptors. Role of guanosine triphosphate binding proteins in regulation of potassium permeability

The involvement of GTP binding proteins in muscarinic acetylcholine receptor (mAChR) mediated responses of cultured chick embryonic cardiac muscle cells was studied by using islet activating protein (IAP) from Bordetella pertussis. Incubation of cells for 24 h with IAP resulted in inhibition of subsequent IAP-catalyzed incorporation of [alpha-32P]ADP-ribose into membrane proteins of Mr 39 000 (No alpha) and 41 000 (Ni alpha); treatment of cultures with 5 ng/mL IAP was sufficient to ADP-ribosylate all available No alpha and Ni alpha. Inhibition of forskolin-stimulated cAMP accumulation by the muscarinic agonist carbachol was abolished in cultures pretreated with IAP. The affinity of carbachol for the mAChR in membranes from IAP-treated cells was considerably decreased compared to control membranes and was not further decreased by addition of guanyl-5'-yl imidodiphosphate. In contrast, the affinity of carbachol for the mAChR on intact cells was not affected by pretreatment with IAP. To investigate the involvement of No and/or Ni in mAChR-mediated increases in K+ permeability, the effect of IAP treatment on mAChR stimulation of 86Rb+ efflux was determined. Treatment of cultures with 5 ng/mL IAP for 24 h completely blocked the stimulation of 86Rb+ efflux evoked by carbachol. Because previous work has shown that mAChR regulation of K+ permeability is independent of changes in cAMP levels, these results suggest a role for No and/or Ni in coupling the mAChR directly to K+ channels in the heart.