Mathematical model of the activation of prothrombin by factor X a and factor V t

A mathematical model of prothrombin activation is being proposed which includes the feedback mechanism of thrombin and the alteration of factor V by thrombin. This model is in good agreement with experimental data for the dependence of the rate of thrombin formation on the concentrations of factors V and X _a . In particular, it correctly predicts the existence and location of a maximum in both of these cases.     

Characterization of cloned chicken anemia virus DNA that contains all elements for the infectious replication cycle.

Circular double-stranded replication intermediates were identified in low-molecular-weight DNA of cells of the avian leukemia virus-induced lymphoblastoid cell line 1104-X-5 infected with chicken anemia virus (CAV). To characterize the genome of CAV, we cloned linearized CAV DNA into the vector pIC20H. Transfection of the circularized cloned insert into chicken cell lines caused a cytopathogenic effect, which was arrested when a chicken serum with neutralizing antibodies directed against CAV was added. Chickens inoculated at 1 day of age with CAV collected from cell lines transfected with cloned CAV DNA developed clinical signs of CAV. The 2,319-bp cloned CAV DNA contained all the genetic information needed for the complete replication cycle of CAV. The CAV DNA sequence has three partially overlapping major reading frames coding for putative peptides of 51.6, 24.0, and 13.6 kDa. The CAV genome probably contains only one promoter region and only one poly(A) addition signal. Southern blot analysis using oligomers derived from the CAV DNA sequence showed that infected cells contained double- and single-stranded CAV DNAs, whereas purified virus contained only the minus strand. It is the first time that the genome of one of the three known single-stranded circular DNA viruses has been completely analyzed.     

Potassium Accumulation and Permeation in the Canine Carotid Artery

Potassium accumulation was studied in slices equilibrated in solutions of varying potassium concentration ([K](ex) = 0-20 mM). Steady-state (42)K uptake was also measured under similar conditions. The accumulated potassium characterized by slow exchange kinetics (half time more than 25 min) exhibited saturation behavior at high external concentrations (maximum, 119 meq/kg dry solid), and exhibited cooperative interaction with sodium. Values calculated from an adsorption isotherm based on solute-protein interaction in a fixed charge system were in agreement with the experimental results. Rubidium competitively inhibited the accumulation of potassium. Studies of the (42)K flux indicated that the rate constants for the slow component decreased with increasing [K](ex). At [K](ex) = 3.33 mM a minimum of about 0.88 x 10(-4) sec(-1) was reached. The potassium flux exhibited saturation behavior at high [K](ex) (maximum 10.5 x 10(-3) meq/kg d.s. per sec). A diffusion coefficient of 1.1 x 10(-5) cm(2) sec(-1) adequately characterized the fast exchanging potassium. A portion of this component exhibited saturation behavior (maximum, 11 meq/kg d.s.) and followed the Langmuir adsorption isotherm. The properties exhibited by potassium accumulation and permeation processes were consistent with those of a fixed charge system as formulated in the "association-induction hypothesis." It is suggested that this model provides an analytical basis for future experimentation.     

Note on the glycolytic coefficient

The glycolytic coefficient of a cell is expressed as a function of the external concentrations of glucose, lactic acid and oxygen. It is shown that this function has a smallest value when the external concentration of glucose is zero and a certain inequality between the external concentrations of lactic acid and of oxygen is satisfied.     

Blood flow in branching circulatory systems during rest and activity

On the basis of simple physical considerations the blood flow in a branching circulatory system is studied. The case of two groups of parallel vessels is treated. The vessels of the same group are supposed to be identical. The resistance of each group is determined by the resistance of each vessel in the group and by the number of vessels in the group. From the dependence of the resistance of each vessel on its radius an expression is obtained for the blood flow through each group of vessels in terms of the numbers and sizes of the vessels in each group. The number of open vessels in an organ and the radius of each of those vessels are assumed to depend on the metabolic rate of that organ. The relations so obtained, together with the expression above, are applied to derive the blood flow through an organ as a function of the metabolic rate of that organ. It is indicated that the relations obtained might describe the shifting of blood from one organ to another if the activity of one of them changes. A way is pointed out to treat neural regulation of this phenomenon.     

Mild cycles open closed communities to ecological restoration

Species loss is a global issue. With up to a million species at risk and insufficient protected area to maintain the world's biodiversity, humanity will increasingly need to rely on species re‐introductions to locally restore diversity and function. However, such restoration attempts are bound to fail when ecological communities get locked in a closed state that is resistant to recovery. It is presently unknown how to repair these closed systems. We use mathematical models to identify ways out of this problem. We first show how ecological communities may enter a closed state, to then explain how to open them up again for restoration of their original diversity. We find that restoration is often still possible shortly after initial species loss, as (1) the secondary extinctions that produce closure have not happened yet and (2) mild population fluctuations still allow successful repair during a transient postdisturbance phase. However, after this typically short window of opportunity for restoration, the system enters a new equilibrium, which may be a closed state. Our analysis shows how to take ecological communities out of the closed state: Appropriate management of carrying capacities produces a regime of mild population fluctuations that opens a window for successful species re‐introductions. These windows can be perpetually recurring or permanently open. Such opportunities for repair can be absent under regimes of wild cycles or perfect stability. We conclude that mild cycles may open windows of opportunity for the repair of communities that have become resistant to recovery.     

AiO,combining DNA/protein programs and oligo-management

SUMMARY: AiO (All in One) is a program for Windows, that combines typical DNA/protein features such as plasmid map drawing, finding of ORFs, translate, backtranslate and high quality printing with a number of databases. These databases allow the management of oligonucleotides, oligonucleotide-manufacturers, restriction enzymes, structural DNA and program users in a multi-user/multi-group environment. AVAILABILITY: An AiO specific website, with the possibility to download is at: http://134.99.88.55/aio/ SUPPLEMENTARY INFORMATION: Examples with screen shots- http://134.99.88.55/aio/ : Manual (in PDF format)-http://134.99.88.55/aio/manual.pdf     

On the adsorption of ions at charged sites in an electric field: I

Considering only nearest neighbor interactions, an expression is obtained for the grand partition function for the adsorption of two kinds of monovalent positive ions at a long chain of one type of monovalent negative fixed sites in an electric field. Expressions are obtained for the fractions of sites which are occupied by each kind of ion as well as of those which are unoccupied as a function of the potential of the electric field.     

Distinct mechanisms eliminate mother and daughter centrioles in meiosis of starfish oocytes

Centriole elimination is an essential process that occurs in female meiosis of metazoa to reset centriole number in the zygote at fertilization. How centrioles are eliminated remains poorly understood. Here we visualize the entire elimination process live in starfish oocytes. Using specific fluorescent markers, we demonstrate that the two older, mother centrioles are selectively removed from the oocyte by extrusion into polar bodies. We show that this requires specific positioning of the second meiotic spindle, achieved by dynein-driven transport, and anchorage of the mother centriole to the plasma membrane via mother-specific appendages. In contrast, the single daughter centriole remaining in the egg is eliminated before the first embryonic cleavage. We demonstrate that these distinct elimination mechanisms are necessary because if mother centrioles are artificially retained, they cannot be inactivated, resulting in multipolar zygotic spindles. Thus, our findings reveal a dual mechanism to eliminate centrioles: mothers are physically removed, whereas daughters are eliminated in the cytoplasm, preparing the egg for fertilization.