Characterization of recombinant polioviruses expressing regions of rotavirus VP4, hepatitis B surface antigen, and herpes simplex virus type 2 glycoprotein D.

Recombinant polioviruses expressing antigens from rotavirus, herpes simplex virus type 2, and hepatitis B virus were generated. Fusion of the heterologous polypeptides to the amino terminus of the poliovirus polyprotein did not prevent myristylation of VP0, suggesting a novel mechanism of myristylation for these recombinant viruses. The effects of the parental genetic background, different foreign sequences, and different insert sizes on growth characteristics were compared. Both the size and the nature of the heterologous sequence appeared to be factors influencing the growth and stability of recombinant polioviruses. All of the recombinants showed a temperature-sensitive phenotype, regardless of the genetic background (attenuated or wild type) from which they were derived. Preliminary studies with transgenic mice carrying the poliovirus receptor gene are discussed.     

Symbiotic growth of Acetobacter suboxydans and Saccharomyces carlsbergensis in a chemostat

The bacterium Acetobacter suboyxdans and the yeast Saccharomyces carlsbergensis have been grown together on a synthetic medium in a chemostat. Mannitol, the only carbon source fed to the fermenter, is oxidized by the bacteria to fructose. The yeast, which cannot attack mannitol, breaks down the fructose nearly completely. Eight steady states and five transitory periods after changes in flow rate have been analyzed to study the kinetics of the mixed culture. Separate cell concentrations were determined by a modified Coulter counter apparatus. Both sugars were monitored. Both bacteria and yeast may be modeled using Monod's equation, the latter with some deviations. The yeast is unable to grow beyond the washout point of the bacteria, even though its maximum growth rate is much higher. The yield of both organisms decreases with increasing dilution rate, as does their average cell size. After step changes in dilution rate, repeated oscillations of both sugar and cell concentrations usually occur before steady-state conditions are reattained. They are generally in phase, with no definite sign of a lag. Oscillations of yeast and fructose concentrations are more pronounced. Periods average about 6 hr and are not correlated with fermentation conditions or equipment variables. Repeated oscillations are not found after step-downs in pure cultures of A. suboxydans, leading to the conclusion that the instability in mixed cultures may be caused by a feedback mechanism from the yeast to the bacteria.     

Selective Replication of Bacteriophage φ29 Deoxyribonucleic Acid in 6-(p-Hydroxyphenylazo)-Uracil-Treated Bacillus subtilis

Phage phi29 deoxyribonucleic acid (DNA) replicated under conditions where semiconservative DNA production in Bacillus subtilis host cells was blocked with 6-(p-hydroxyphenylazo)-uracil (HPUra). The time of initiation of phi29 DNA replication was not affected by HPUra, and normal quantities of viable phage were produced in the presence of the inhibitor. Studies with conditional lethal mutants of phage phi29 demonstrated the usefulness of HPUra for detection of viral-specific DNA production.     

Phospholipid metabolism of stimulated lymphocytes: Comparison of the activation of acyl-CoA: Lysolecithin acyltransferase with the binding of concanavalin A to thymocytes

Calf thymocytes were isolated and incubated with concanavalin A. The effect of the mitogen on the enzyme activity of membrane-bound lysolecithin acyltransferase (acyl-CoA: $\text{1-acylglycero-3-phosphorylcholine}\text{-O-}\text{acyltransferase}$, EC 2.3.1.23) was determined as also the binding of ¹²⁵I-labelled concanavalin A to intact cells and isolated membranes.The lysolecithin acyltransferase was found to be activated three times in microsomal membranes. The activation occurred directly after binding of concanavalin A and was temperature independent, since similar activities were found in cells treated with concanavalin A at 0 and 37 °C.The acyltransferase activation using increasing concentrations of concanavalin A revealed a different behaviour, as compared to the binding of concanavalin A. While the binding of concanavalin A to intact cells expressed a normal hyperbolic saturation function the activation process of the acyltransferase described a sigmoidal relationship. Corespondingly, the interaction coefficients for both functions were different (Sips coefficient for binding = 1.0 and Hill coefficient of the enzyme activation = 1.8).These results indicate that the acyltransferase activation is due to a cooperative interaction between the ligand-receptor complex and the enzyme.     

Estimation of intrinsic kinetic constants for pore diffusion-limited immobilized enzyme reactions

A simple method is presented that establishes intrinsic rate parameters when slow pore diffusion of substrate limits immobilized enzyme reactions that obey Michaelis-Menten kinetics. The Aris-Bischoff modulus is employed. Data at high substrate concentrations, where the enzyme would be saturated in the absence of diffusion limitation, and at low substrate concentrations, where effectiveness factors are inversely proportional to reaction modulus, are used to determine maximum rate and Michaelis constant, respectively. Because Michaelis-Menten and Langmuir-Hinshelwood kinetics are formally identical, this method may be used to estimate intrinsic rate parameters of many heterogeneous catalysts. The technique is demonstrated using experimental data from the hydrolysis of maize dextrin with diffusion-limited immobilized glucoamylase. This system yields a Michaelis constant of 0.14%, compared to 0.11% for soluble glucoamylase and 0.24% for immobilized glucoamylase free of diffusional effects.     

The elastic and ultimate properties of compact bone tissue

The use of a tranversely isotropic model is tested for the elastic behavior of bovine and human bone and the five independent constants of this model are determined. The accuracy of the model is tested for eight cases by comparing the off-axis modulus predicted by a rotation of stiffness matrix with an experimentally determined off-axis modulus.

Ultimate properties are presented for bovine and human bone for tension, compression, and torsional loads. A Hankinson type failure criterion is proposed for off-axis ultimate stress and this predicted value compared with experimental values for nine cases.