Use of lac operon fusions to isolate Escherichia coli mutants with altered expression of the fumarate reductase system in response to substrate and respiratory controls.

Strains of $\text{E}\text{.}\text{coli}$ with fusions between the $\text{lac}$ structural genes and the promoter region of the fumarate reductase system were constructed from a parental strain deleted in the native $\text{lac}$ operon. Like fumarate reductase in wild-type cells, β-galactosidase in these fusion strains is inducible by fumarate, but only under anaerobic conditions. From one of these strains, three classes of mutants altered in the expression of the hybrid operon were isolated. By anaerobic selection for growth on lactose in the absence of fumarate, mutants that synthesize β-galactosidase constitutively both aerobically and anaerobically were obtained. By aerobic selection for growth on lactose in the presence of fumarate, mutants that are inducible in the enzyme both aerobically and anaerobically and mutants that are inducible in the enzyme only aerobically were obtained. The regulatory behaviors of the mutants studied suggest that substrate and respiratory control of the expression of the fumarate reductase complex are mechanistically connected.     

Clonal growth in vitro by mouse Kupffer cells.

Mouse liver Kupffer cells were induced to proliferate and form discrete colonies of mononuclear phagocytes in vitro. These colony-forming cells from the liver are similar to other mononuclear phagocyte colony-forming cells in that they require a colony-stimulating factor present in medium conditioned by L cells for proliferation in vitro. Cells in the colonies were phagocytic and had IgG receptors on the membrane. For this class of colony-forming cells, the D₀ value to gamma irradiation in vitro was 108 rads.     

ZINC AND COPPER TOLERANCE OF AGROSTIS STOLONIFERA L. IN TISSUE CULTURE

Callus tissue was induced from shoot meristematic tissue and root tips of a clone of the grass Agrostis stolonifera tolerant to both zinc and copper, and from a control clone tolerant to neither metal. Growth of the callus tissue on media containing zinc and copper showed that tolerance to both metals was maintained in tissue culture. The pattern of metal uptake in tissue culture resembled uptake by whole plants in that tolerant tissue took up more metal than nontolerant tissue. Plants regenerated from callus had the same copper and zinc tolerance as the original parental clones regardless of time of growth in tissue culture and shoot or root origin of the tissue. The results support previous evidence that metal tolerance is genetically determined and acts at the cellular level.     

Nonlinear diffusion in biological systems

Diffusion problem with variabale diffusion coefficient in a spherical biological system is investigated. Also included in this study is the biological reaction of the Michaelis-Menten type. The problem formulated consists of a highly nonlinear differential equation which, however, can be efficiently solved by the orthogonal collocation method on a digital computer. The effects of the dimensionless governing parameters on the transient and steady state concentration responses are parametrically examined for the diffusion system with and without biological reaction.     

蚕氨基酸代谢的研究——家蚕与蓖麻蚕的氨基酸和形成甘氨酸、丙氨酸的酶系比较及酮丙二酸的脱羧作用

家蚕(Bombyx mori L.)与蓖麻蚕(Samia,ricini B)的丝蛋白氨基酸含量差异甚为显著;家蚕丝含量最多的为甘氨酸(42.8％),其次为丙氨酸(32.4％);而蓖麻蚕丝则以两氨酸含量为最高(50.5％),其次为甘氨酸(27.8％)(Kirimuru等,1962)。为了阐明丝蛋白主要氨基酸的形成机制,我们曾报道了这两种蚕丝腺中,自L-天门冬氨酸与α-酮戊二酸形成丙氨酸的机制(许延森等,1964a);体液乙醛酸及丙酮酸与丝蛋白相应氨基酸的含量之     

Isolation of two proteins with 9-ketoprostaglandin reductase and NADP-linked 15-hydroxyprostaglandin dehydrogenase activities and studies on their inhibition

Two proteins containing 9-ketoprostaglandin reductase and NADP-linked 15-hydroxyprostaglandin dehydrogenase activities have been isolated. Both of these activities are inhibited by a low molecular weight placental protein and by indomethacin, ethacrynic acid, and furosemide.     

Dynamic light-scattering studies of internal motions in DNA. I. Applicability of the rouse-zimm model

The intermediate scattering function G(K,t) for any polymer model obeying a linear separable Langevin equation can be expressed in terms of the eigenvalues and eigenvectors of its normal coordinate transformation. An algorithm for the extract numerical evaluation of G(K,t) for linear Rouse-Zimm chains in the presence of hydrodynamic interaction has been developed. The computed G(K,t)² were fit to C(t) = A exp(?t/τA) + B, and apparent diffusion coefficients calculated according to D_app ≡ 1/(2τ_AK²). G(K,t)² was surprisingly well-fit by single-exponential decays, especially at both small and large values of Kb, where K is the scattering vector and b the root-mean-squared subunit extension. Plots of D_app vs K² in-variably showed a sigmoidal rise from D₀ at K² = O up to a constant plateau value at large K²b². Analytical expression for G(K,t), exact in the limit of short times, were obtained for circular Rouse-Zimm chains with and without hydrodynamic interaction, and also for free-draining linear chains, and in addition for the independent-segment-mean-force (ISMF) model. The predicted behaviors for G(K,t) at large Kb (or KR_G) was found in all cases to be single-exponential with 1/τ ∝ K² at large Kb, in agreement with the computational results. A simple procedure for estamating all parameter of the Rouse-Zimm model from a plot of D_app vs K² is proposed. Experimental data for both native and pH-denatured calf-thymus DNA in 1.0M Nacl with and without EDTA clearly plateau behavior of D_app at large values of K, in harmony with the present Rouse-Zimm and ISMF theories, and in sharp contrast to previous predictions based on the Rouse-Zimm model.     

Brownian motion of highly charged poly(L-lysine). Effects of salt and polyion concentration

The Brownian motion of a single sample of high-molecular-weight poly(L -lysine) [(Lys)_n, n = 955] has been studied by dynamic light scattering over a wide range of NaBr concentrations and at three different polyion concentrations. A substantial decrease in scattered intensity is associated with the transition from the ordinary phase to the low-salt extraordinary phase. At the salt concentration where the transition takes place the relaxations are non-exponential and appear to exhibit at all angles a rapid relaxation (τ ? 10 μsec) that is presumed to be a manifestation of the kinetics of the transition process. The K² dependence of the slow relaxation rates in the extraordinary phase has been confirmed within the experimental error. The extrapolated infinite-dilution values of the diffusion coefficients in the ordinary phase are observed to decline precipitously below 10^?2M salt to astonishingly small values, indicating a dramatic rise in the friction factors of the isolated polyions. An extensive discussion of these findings in relation to the theory employed here and to existing data in the literature is also given.