Control of mixed-substrate utilization in continuous cultures of Escherichia coli

The chemostat culture technique was used to study the control mechanisms which operate during utilization of mixtures of glucose and lactose and glucose and l-aspartic acid by populations of Escherichia coli B6. Constitutive mutants were rapidly selected during continuous culture on a mixture of glucose and lactose, and the beta-galactosidase level of the culture increased greatly. After mutant selection, the specific beta-galactosidase level of the culture was a decreasing function of growth rate. In cultures of both the inducible wild type and the constitutive mutant, glucose and lactose were simultaneously utilized at moderate growth rates, whereas only glucose was used in the inducible cultures at high growth rates. Catabolite repression was shown to be the primary mechanism of control of beta-galactosidase level and lactose utilization in continuous culture on mixed substrates. In batch culture, as in the chemostat, catabolite repression acting by itself on the lac enzymes was insufficient to prevent lactose utilization or cause diauxie. Interference with induction of the lac operon, as well as catabolite repression, was necessary to produce diauxic growth. Continuous cultures fed mixtures of glucose and l-aspartic acid utilized both substrates at moderate growth rates, even though the catabolic enzyme aspartase was linearly repressed with increasing growth rate. Although the repression of aspartase paralleled the catabolite repression of beta-galactosidase, l-aspartic acid could be utilized even at very low levels of the catabolic enzyme because of direct anabolic incorporation into protein.     

Staphylococcal Hyaluronate Lyase: Purification and Characterization Studies

Staphylococcal hyaluronate lyase (hyaluronidase) derived from a pathogenic strain of staphylococcus was purified by means of salt fractionation with ammonium sulfate and gel filtration through Sephadex G-100. Most of the enzyme activity from concentrated culture supernatant fluids of staphylococci was obtained in a fraction precipitated by 90 to 100% saturation with ammonium sulfate. A small amount of enzyme was also precipitated by 80 to 90% saturation with the salt. The hyaluronidase-rich fractions did not contain other staphylococcal enzymes, such as coagulase, protease, lipase, and staphylokinase. These enzymes were present in the original concentrates. Molecular sieving chromatography of the partially purified enzyme by filtration through Sephadex G-100 resulted in a further increase in specific enzyme activity. However, more than one active peak was obtained after gel filtration, thus suggesting that there may be more than one molecular form of the enzyme. Immunodiffusion in agar gel of the chromatographically purified enzyme fraction, with immune serum from rabbits injected with concentrated staphylococcal culture supernatant fluids, indicated that there was one major antigen. A similar antigen, giving reactions of identity with the purified material, was present in the original culture supernatant fluid.     

Efficiency and the Public's Health

The Governor''s Survey on Efficiency and Cost Control, established by Governor Reagan''s executive order, was a non-profit, bipartisan, privately financed management analysis of State administration conducted by private citizens, including physicians, during 1967 for the purpose of achieving improvement in administrative procedure and operating economies in State government.State employees and appointed department heads offered many valuable suggestions and cooperated fully with the survey team.Two hundred recommendations were submitted to the Governor for improvement in the Departments of Public Health and Mental Hygiene, the Office of Health Care Services and the organizations under the Secretary of Human Relations.The recommendations for the health-related administrative units concerned reorganization and consolidation of departments and units, improvement in administrative and operating methods and improvement of services. Annual savings of several hundred million dollars could result.None of the recommendations were for reduction in services and none concerned individual employees or appointees.Assistance in and support for the implementation of the recommendations will be needed from legislators, responsible citizens and organizations interested in efficient and economical government.     

Novel heparin degradation products. Isolation and characterization of novel disaccharides and oligosaccharides produced from heparin by bacterial degradation

1. Heparin was degraded by enzymes of adapted Flavobacterium heparinum. Several degradation products were separated by combined Sephadex-gel filtration and paper chromatography, and chemically analysed. 2. These products were identified as glucosamine 2,6-disulphate, saturated disaccharides constituted of uronic acid and glucosamine and containing two and three sulphate residues, and tetra- and hexa-saccharides with the same basic disaccharide units. 3. The implications of these findings with respect to the present knowledge of heparin structure and its enzymic degradation are discussed.     

Statistical-Mechanical Studies of the α ⇄ β Transformation in Keratins: II. The Tension-Length Isotherms

In attempting to understand the yield region of the α β transformation in keratins (Astbury and Woods, 1933), we recently proposed a statistical-mechanical model (David and Schor, 1965) which generalized the work done by others on the helix random coil transformation (Zimm and Bragg, 1959; Gibbs and DiMarzio, 1959) (thermal denaturation) to the case of a polypeptide under external tension (Birstein, 1962). We wish now to report the comparison of the quantitative aspects of this model to the observed tension-length isotherms (in the yield region) of Cotswold wool.     

Electric Impedance and Rectification of Fused Anion-Cation Membranes in Solution

At relatively high currents, fused anion-cation membranes give rise to rectifying and reactive effects. The rectification becomes less pronounced with increasing frequency. This effect results from changes in the concentration profiles of the ions during the positive and negative phases of the AC cycle. With reduction of the current, the voltage-current response becomes linear. The reactive effect can then be separated from the rectifying effect. The former effect can be attributed essentially to two factors: (a) the presence of transition regions of fixed charge and (b) the diffusion mechanism of the ions in an AC field. The first factor is largely frequency-independent and the second, frequency-dependent. A first approximation equivalent circuit is described. This circuit involves frequency-dependent elements.