Characterizing Attention with Predictive Network Models.

Recent work shows that models based on functional connectivity in large-scale brain networks can predict individuals' attentional abilities. While being some of the first generalizable neuromarkers of cognitive function, these models also inform our basic understanding of attention, providing empirical evidence that: (i) attention is a network property of brain computation; (ii) the functional architecture that underlies attention can be measured while people are not engaged in any explicit task; and (iii) this architecture supports a general attentional ability that is common to several laboratory-based tasks and is impaired in attention deficit hyperactivity disorder (ADHD). Looking ahead, connectivity-based predictive models of attention and other cognitive abilities and behaviors may potentially improve the assessment, diagnosis, and treatment of clinical dysfunction.

Preparation and characterization of an enzymatically active immobilized derivative of myosin.

Purified skeletal muscle myosin (EC 3.6.1.3) has been covalently bound to Sepharose 4B by the cyanogen bromide procedure. The resulting complex, Sepharose-Myosin, possesses adenosine triphosphatase activity and is relatively stable for long periods of time. Under optimal binding conditions, approximately 33% of the specific ATPase activity of the bound myosin is retained. Polyacrylamide gel electrophoresis of polypeptides released from denatured Sepharose-Myosin indicates that 85% of the myosin is attached to the agarose beads through the heavy chains and the remainder through the light chains, in agreement with predictions of binding and release based upon either the lysine contents or molecular weights of themyosin subunits. The adenosine triphosphatase of the immobilized myosin has been investigated under conditions of varying pH, ionic strength, and cation concentration. The ATPase profiles of immobilized myosin are quite similar to those for free myosin, however subtle differences are found. The Sepharose-Myosin ATPase is not as sensitive as myosin to alterations in salt concentration and the apparent KM is approximately two-fold higher than that of myosin. These differences are probably due to chemical modification in the region of the attachment site(s) to the agarose beads and hydration and diffusion limitations imposed by the polymeric agarose matrix.

Purification and characterization of an extracellular ATPase from oviductal secretions.

Oviductal secretions include an ATPase (EC 3.6.1.3) that is transferred from the outer surface of the secretory cells to the surface of the ovulated oocyte. The enzyme has been purified and is a highly labile, very high molecular weight lipoprotein complex (greater than 4-10(6)). It consists of 47% protein and 53% lipid. Lipid composition is limited to phosphatidylcholine, phosphatidylethanolamine and sphingomyelin. The basic protein subunit has a molecular weight of 170 000. The enzyme exhibits many of the characteristics of ectoenzyme ATPase. The enzyme is Mg2+ or Ca2+ dependent; the Mg2+-ATPase has pH optima at 6.0 and 7.8 and the Ca2+-ATPase at 9.0. Substrate specificity is limited to ATP with lesser activity towards GTP, CTP, UPT and ADP. Km for ATP is 0.88 mM and the enzyme is inhibited at substrate concentrations greater than 3 mM ATP.

Characterization of cellular attachment and spreading molecules at liquid-liquid interfaces.

Cells are grown at a liquid-liquid interface (ultrafiltrate of growth medium--heptacosafluorotributylamine). Following attachment and spreading an intermediate-density, isotonic solution of metrizamide-Ficoll is introduced. Cells are detached by centrifugation at 150,000g X 45 min. Molecules deposited at the interface are removed and examined by gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals 20 protein bands ranging in molecular weight from 30,000 to 200,000. Most bands have molecular weights less than 120,000. The substrate-attached material contains approximately 2.8 pg of protein per attached cell. Substrate-attached molecules can be removed without detergent denaturation for additional studies.

Characterization of a protein kinase from chicken oviductal fluids.

Protein kinase has been found extracellularly in avian oviductal secretions. The enzyme has been isolated and shown to be primarily type II cAMP enhanced. The Ka for cAMP activation, binding and elution from ion-exchange columns, molecular weight of subunits, pH optimum as a histone kinase, response to cations, kinetic properties, and preference for lysine-rich histone are similar to those of mammalian type II protein kinase. Gel filtration data suggest that the dimer form is the functional entity in the reproductive tract. The catalytic subunit has been purified to greater than 90% homogeneity and has a Km of 4 mumol/l and Vmax of 10(6) U/mg, comparable to published values for bovine catalytic subunit.

Adenosine triphosphatase activity at the external surface of chicken brain synaptosomes.

An ATP-hydrolysing activity on the external surface of intact synaptosomes from chicken forebrain has been investigated. The observed ATPase activity was not due to leakage of the intracellular ATPase activities, of artefacts resulting from breakage of the nerve endings during the incubation and isolation periods, or to possible contamination by other subcellular particles. Disruption of the synaptosomes resulted in an approximately 2.5-fold increase of the basal, Mg2+-dependent ATPase activity, suggesting that the plasma membrane was acting as permeability barrier to the substrate. ATP hydrolysis was maximal (0.8 mumol Pi/min/mg protein) at pH 8.2 in a medium containing either Mg2+ or Ca2+ ions. Ouabain (0.2 mM) and oligomycin (2 micrograms/mg protein) had no appreciable effect on this ATPase activity. Kinetic studies of the enzyme revealed an apparent Km value of ATP of approximately 4 x 10(-5) M. These data are consistent with the view that the observed ATP hydrolysis was being catalysed by an ectoenzyme, i.e., an enzyme in the plasma membrane of the nerve endings with its active site facing the external medium. The rapid hydrolysis of the released ATP is a suspected function for this ecto-ATPase.

Binding to cell surfaces by antibodies against exoATPase.

Avian oviductal secretions contain an exoATPase which has been purified up to 900-fold. Antibodies to this fraction bind to several cell types and to membrane fractions solubilized by selected detergents. The experiments indicate that a related antigen is present in plasma membranes and that exoATPase is released by a shedding process.

Phosphorylating-dephosphorylating enzymes of avian oviductal secretions.

Avian oviductal fluids contain phosphorylating-dephosphorylating enzymes that might function in sperm-oocyte interactions. Phosphorprotein phosphatase and protein kinase have been purified 20-fold and 40-fold, respectively. The latter easily aggregates and is highly labile. Other properties are comparable to those of holoenzymes.

Concurrent sex partners and risk for sexually transmitted diseases among adolescents.

BACKGROUND/OBJECTIVES: A large percentage of sexually active adolescents have multiple sex partners and are at high risk of acquiring sexually transmitted diseases (STDs). Little is known about adolescents' patterns of sexual partnerships (e.g., concurrent versus serial) and how these patterns influence STD risk. GOAL OF THE STUDY: To determine the frequency with which adolescents have concurrent partners during a main relationship and the association between having concurrent partners and STD risk. STUDY DESIGN: Adolescents seeking care at a public STD clinic were recruited from March, 1996, to May, 1998. Demographic and behavioral data were obtained during an interviewer-administered questionnaire. Sexually transmitted disease testing and physical exams were performed by clinicians. RESULTS: Of those adolescents who reported having at least one main partner during the previous 6 months (n = 245), 110 (44.9%) had multiple partners, and 76 (31%) had at least one concurrent partner during a main relationship. Greater number of concurrent partners was associated with STD diagnosis/exposure after controlling for number of sex partners (OR = 1.6; 95% CI, 1.1-2.4). CONCLUSIONS: A significant percentage of adolescents have concurrent partners during a main relationship, and having concurrent partners increases STD risk.

Chicken oviductal ecto-ATP-diphosphohydrolase. Purification and characterization.

An ecto-ATP diphosphohydrolase (ATPDase) was purified to homogeneity from vesiculosomes shed from chicken oviduct. First, the ecto-ATPDase-enriched vesiculosomes were concentrated by filtration, differential centrifugation, and exclusion chromatography. Next, the nonionic detergent, Nonidet P-40, was used to extract the ecto-ATPDase from vesiculosomal membranes, and the solubilized enzyme was further purified by ion exchange (DEAE-Bio-Gel) and lentil-lectin-Sepharose 4B chromatography. In the final stage, immunoaffinity chromatography was utilized to obtain purified ecto-ATPDase. More than 25,000-fold purification was achieved. Specific activity of the purified enzyme was greater than 800 micronol/min/mg of protein with MgATP as the substrate, the highest ever reported for an ATPDase. The enzyme also hydrolyzed other nucleoside triphosphates in the presence of magnesium at similar rates and CaATP and MgADP at lower rates. The molecular mass of the purified glycoprotein was 80 kDa as determined by SDS-polyacrylamide gel electrophoresis and Western blot analysis. Based on its enzymatic properties, the relationship of the chicken oviduct ecto-ATPDase with other reported ATPDases and ecto-ATPases is discussed.

Resonance transduction of low level periodic signals by an enzyme: an oscillatory activation barrier model.

The overall rate of an enzyme catalyzed reaction is determined by the activation barrier of a rate-limiting step. If the barrier is oscillatory due to the intrinsic properties of a fluctuating enzyme, this enzymatic reaction will be influenced by a low level periodic electric field through the resonance transduction between the applied field and the oscillatory activation barrier. The ATP hydrolysis activity of a highly purified, detergent solubilized Ecto-ATPase from chicken oviduct was used to test the above concept. At 37 degrees C, this activity (1,800 mumols mg-1 min-1) was stimulated up to 47% (to 2,650 mumols mg-1 min-1) by an alternating electric field (AC), with a frequency window at 10 kHz. The maximal stimulation occurred at 5.0 V (peak-to-peak) cm-1. The potential drop across the dimension of the enzyme was approximately 10 microV (micelle diameter 20 nm). The activation barrier, or the Arrhenius activation energy, of the ATP splitting was measured to be 30 kT and the maximal barrier oscillation was calculated to be approximately 2.5 kT according to the oscillatory activation barrier (OAB) model. With the optimal AC field, full impact of the electric stimulation could be effected in much less than a second. The OAB model is many orders of magnitude more sensitive for deciphering low level periodic signals than the electroconformational coupling (ECC) model, although the latter has the ability to actively transduce energy while the former does not. By the OAB mechanism, the detecting limit of an external electric field by the ATPase, in a cell 20 micro m in diameter,would be 5 mV cm-1, but could be much lower for other membrane enzymes or receptors (e.g., nV cm-1). We propose that mechanisms similar to the OAB model could explain how a weak electromagnetic field or acoustic noises can exert its effects on an organism or a living cell.

Ion channel enzyme in an oscillating electric field.

To explain the electrical activation of several membrane ATPases, an electroconformational coupling (ECC) model has previously been proposed. The model explained many features of experimental data but failed to reproduce a window of the field intensity for the stimulated activity. It is shown here that if the affinities of the ion for the two conformational states of the transporter (one with binding site on the left side and the other on the right side of the membrane) are dependent on the electric field, the field-dependent transport can exhibit the observed window. The transporter may be described as a channel enzyme which opens to one side of the membrane at a time. It retains the energy-transducing ability of the earlier ECC models. Analysis of the channel enzyme in terms of the Michaelis-Menten kinetics has been done. The model reproduced the amplitude window for the electric field-induced cation pumping by (Na,K)-ATPase.