The effect of maternal employment on adolescents' transition to young adulthood

The purpose of this study was to examine relationships between multiple characteristics of maternal employment, parenting practices, and adolescents’ transition outcomes to young adulthood. The research addressed four main research questions. First, are the characteristics of maternal work (i.e., hours worked, multiple jobs held, work schedules, earnings, and occupation) related to adolescents’ enrollment in post-secondary education, employment, or involvement in neither of these types of activities as young adults? Second, are the work characteristics related to parental involvement and monitoring, and are the parenting practices related to adolescents’ transition outcomes? Third, do parental involvement and monitoring mediate any relationships between the characteristics of maternal employment and adolescents’ transition outcomes? Finally, do any associations between characteristics of maternal employment and parenting practices and adolescents’ transition outcomes vary by poverty status, race/ethnicity, or gender? To address these research questions, secondary data analysis was conducted, using data from the National Longitudinal Survey of Youth (NLSY) from 1998 through 2004. The study sample consisted of 849 youths who were 15 through 17 years of age in either 1998 or 2000, and were 19 through 21 years of age when their transition outcomes in young adulthood were measured four years later. Multinomial logistic and ordinary least squares regression models were estimated to answer the research questions. Study findings indicated that of the maternal work characteristics, mothers’ multiple jobs held, occupation, and work schedule were significantly related to the youths’ transition outcomes. When mothers held multiple jobs for 1 to 25 weeks per year, and when mothers held jobs involving lower levels of occupational complexity, their youths were more likely to experience employment rather than post-secondary education. Adolescents whose mothers worked a standard work schedule were less likely to experience other types of transitions than post-secondary education. With regard to the effects of maternal employment on parenting practices, none of the maternal work variables were related to parental involvement, and only one variable, mothers working less than 40 hours per week, was negatively related to parental monitoring. In addition, when parents were more involved with their youths’ education, the youths were less likely to transition into employment and other types of transitions rather than post-secondary education. The parenting practices did not mediate the relation between the significant work variables (holding multiple jobs, work schedule, and occupation) and youths’ transition outcomes. Finally, none of the interactions between maternal work characteristics and poverty status, race/ethnicity, and gender met the criteria for determining significance; but in a series of sub-group analyses, some differences according to poverty status and gender were found. Despite the lack of mediation and moderation, the findings of this study have important implications for social policy and social work intervention. Based on the findings, suggestions are made in these areas to improve working mothers’ lives and their adolescents’ development and successful transition to adulthood. Finally, directions for future research are discussed.

Investigations into the mechanism of orotidine 5'-monophosphate decarboxylase: Sources of substrate destabilization and transition state stabilization

Orotidine 5′-monophosphate decarboxylase (OMPDC) achieves a rarely paralleled rate acceleration, yet the catalytic basis prompting this enhancement have yet to be fully elucidated. To accomplish decarboxylation, OMPDC must overcome the high energy barrier due to the localized anionic charge of the intermediate. Mechanistic studies employing enzyme mutagenesis and product or intermediate analogues were used to investigate possible transition state stabilization by a carbene resonance structure. Viability of the carbene structure depends upon a key hydrogen bond between O4 of the substrate and the amide backbone of a conserved serine or threonine. Substitution of the conserved residue with Pro resulted in a kcat/KM of 1 M-1s-1; deletion of the FUMP O4 resulted in a product analogue that does not undergo H6 exchange or inhibit decarboxylation. Hence, indirect evidence reveals the O4-backbone interaction plays an important role for binding and catalysis. OMPDC likely has honed multiple mechanisms to attain its remarkable catalysis. The successful crystallizations of OMPDC a decade ago sparked hypotheses that structure and sequence conserved residues induced productive strain on the substrate-enzyme complex. Here, we demonstrate a new source of stress: a hydrophobic pocket adjacent to the OMP carboxylate that exhibits kinetic parameters characteristic of substrate destabilization. Substitution of these residues with hydrophilic side-chains, by providing hydrogen-bonding partners, decreased kcat by 10 to 10^4–fold. The same substitutions display very little change in the rate of product H6 exchange, supporting that this hydrophobic pocket affects the substrate-enzyme complex before the transition state. We also provide evidence that hydrophilic residues can insert water molecules into the pocket with detrimental effects to catalysis.

Immune function, gene expression, blood indices and performance in transition dairy cows affected by diet and inflammation

The transition period is associated with the peak incidence of production problems, metabolic disorders and infectious diseases in dairy cows (Drackley, 1999). During this time the cow’s immune system seems to be weakened; it is apparent that metabolic challenges associated with the onset of lactation are factors capable of affecting immune function. However, the reasons for this state are not entirely clear (Goff, 2006). The negative energy balance associated with parturition leads to extensive mobilization of fatty acids stored in adipose tissue, thus, causing marked elevations in blood non-esterified fatty acids (NEFA) and B-hydroxybutyrate (BHBA) concentrations (Drackley et al., 2001). Prepartal level of dietary energy can potentially affect adipose tissue deposition and, thus, the amount of NEFA released into blood and available for metabolism in liver (Drackley et al., 2005). The current feeding practices for pregnant non-lactating cows has been called into question because increasing amounts of moderate-to-high energy diets (i.e. those more similar to lactation diets in the content of energy) during the last 3 wk postpartum have largely failed to overcome peripartal health problems, excessive body condition loss after calving, or declining fertility (Beever, 2006). Current prepartal feeding practices can lead to elevated intakes of energy, which can increase fat deposition in the viscera and upon parturition lead to compromised liver metabolism (Beever, 2006, Drackley et al., 2005). Our general hypothesis was that overfeeding dietary energy during the dry period, accompanied by the metabolic challenges associated with the onset of lactation would render the cow’s immune function less responsive early postpartum. The chapters in this dissertation evaluated neutrophil function, metabolic and inflammation indices and gene expression affected by the plane of dietary energy prepartum and an early post-partum inflammatory challenge in dairy cows. The diet effect in this experiment was transcendental during the transition period and potentially during the entire lactation. Changes in energy balance were observed and provided a good model to study the challenges associated with the onset of lactation. Overall the LPS model provided a consistent response representing an inflammation incident; however the changes in metabolic indices were sudden and hard to detect in most of the cases during the days following the challenge. In general overfeeding dietary energy during the dry period resulted in a less responsive immune function during the early postpartum. In other words, controlling the dietary energy prepartum has more benefits for the dairy cow during transition.