Prediction of enzyme kinetic parameters based on statistical learning

Values of enzyme kinetic parameters are a key requisite for the kinetic modelling of biochemical systems. For most kinetic parameters, however, not even an order of magnitude is known, so the estimation of model parameters from experimental data remains a major task in systems biology. We propose a statistical approach to infer values for kinetic parameters across species and enzymes making use of parameter values that have been measured under various conditions and that are nowadays stored in databases. We fit the data by a statistical regression model in which the substrate, the combination enzyme-substrate and the combination organism-substrate have a linear effect on the logarithmic parameter value. As a result, we obtain predictions and error ranges for unknown enzyme parameters. We apply our method to decadic logarithmic Michaelis-Menten constants from the BRENDA database and confirm the results with leave-one-out crossvalidation, in which we mask one value at a time and predict it from the remaining data. For a set of 8 metabolites we obtain a standard prediction error of 1.01 for the deviation of the predicted values from the true values, while the standard deviation of the experimental values is 1.16. The method is applicable to other types of kinetic parameters for which many experimental data are available

Causal influence in linear response models

The intuition of causation is so fundamental that almost every research study in life sciences refers to this concept. However a widely accepted formal definition of causal influence between observables is still missing. In the framework of linear Langevin networks without feedbacks (linear response models) we developed a measure of causal influence based on a decomposition of information flows over time. We discuss its main properties and compare it with other information measures like the Transfer Entropy. Finally we outline some difficulties of the extension to a general definition of causal influence for complex systems.Comment: 9 pages, 9 figure

Resilience and social support as moderators between financial stressors and strain

A research report submitted to the Faculty of Humanities, University of the Witwatersrand, in partial fulfillment of the requirements of the degree of Master of Arts in Industrial Psychology Johannesburg, 2013This study tested the hypotheses that social support and resilience would each buffer individuals against the potential negative effects of severe financial stressors by moderating the relationship between perceived financial stressor severity and three forms of strain: stress, depression, and anxiety. Correlation and multiple regression analyses were conducted on a sample (N = 580) of clients from a large South African organisation in order to test these hypotheses. Financial stressor severity was assessed using The Stressor Scale. Resilience was measured using The Resilience Scale. Social support was measured using the Multidimensional Scale of Perceived Social Support, and the DASS-21 was used to assess respondents' levels of stress, depression and anxiety. The buffering hypotheses were not supported. Resilience and social support were still significantly negatively associated with perceived stressor severity, as well as subjective reports of stress, anxiety and depression. This indicates that resilience and social support still played a protective role in the stress process, but that they function as antecedent variables as opposed to moderator variables; thereby altering the appraisal of financial stressors and, indirectly, the amount of strain respondents reported feeling as well

Exploring identifiability and status as determinants of intergroup behaviours in virtual interaction.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.Identifiability to an audience is an integral part of social life. It has powerful effects on behaviour. Some authors have argued that “deindividuation”, or a lowered sense of personal identifiability results in a loss of control over individual behaviour in a group situation. However, this has been contested. This study examines the Social Identity Model of Deindividuation Effects (SIDE) and reputational theory as alternatives to traditional models of deindividuation. The SIDE model argues that the salience of personal versus social identity – and therefore the salience of different sets of norms or standards – govern social behaviour, while in contrast, reputational theory suggests that behaviour is governed by a group heuristic which ensures individuals gain and maintain access to generalized systems of exchange. VIAPPL (see www.viappl.org) was used to investigate the effects of various conditions of identifiability on ingroup favouritism, selfishness and reciprocity in an interactive, virtual environment. The results were then examined in order to determine whether the SIDE model or reputational theory were supported

ReSallying Qids: Resilience of queer youth in school.

ReSallying Qids' probed homophobia and heterosexism in school to reveal how Lesbian, Gay, Bisexual, Transgender, Queer-gendered and Queer-sex youth---Qids---were hurt in and by schools and what schools could do to change that. This qualitative study examined; (1) Queer-identity (Q-ID) stressors in the full context of life stress, (2) how Qids dealt with stress, (3) K--12 sites of Q-ID stress, and (4) what schools could do to reflect and celebrate diversity. The study probed new questions yielding interesting responses. Do you remember a time before the closet? and Do you remember entering the closet? Most participants were students still in school. While this created a scarcity of participants, it elicited a credible, contemporary voice concerning Q-gender and Q-sex school experience. Two Lesbians, four Gays, one Fluid, two Bisexuals and one Transsexual took part in a sequence of three narrative-type interviews regarding pain in their lives, things that hurt. While most participants were 13 to 18 years old, one (Transsexual) was 32 and one (Gay male) was eight. Q-ID stressors were more numerous and more intense than other life stressors. Qids applied Q-ID relevant values and strategies in coping with stress. However, of the three protective factor categories of personal characteristics, positive family relations, and external support systems, the later two, if they were present, were unknown and inaccessible to Qids before they left the closet. This absence of supportive people problematized not only Qids' lives but also their being in and coming out of the closet. Adaptations of resilience theory were discussed. Qids saw a need to Feminize, Color, Queer, and diversify schools out of their role of reproducing centers of power. Qids testified that heterodysfunction started early in elementary school where peers policed gender adeptly, even ruthlessly. Qids were often Q-identified and ostracized in or before second or third grade. ReSallying Qids discussed first steps for elementary, middle, and high school communities toward a curriculum and life of diversity liberating for all its members.Ed.D.EducationEducational administrationEducational psychologyEducational sociologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/127622/2/3000912.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/127622/4/license_rd