A new intrinsic thermal parameter for enzymes reveals true temperature optima

Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, Teq, arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source (“evolved”) temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, Teq is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on Teq with respect to enzyme temperature/activity effects to be more important than on thermal stability. Teq is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution

Initial Findings on Visual Acuity Thresholds in an African Elephant (\u3cem\u3eLoxodonta africana\u3c/em\u3e)

There are only a few published examinations of elephant visual acuity. All involved Asian elephants (Elephas maximus) and found visual acuity to be between 8′ and 11′ of arc for a stimulus near the tip of the trunk, equivalent to a 0.50 cm gap, at a distance of about 2 m from the eyes. We predicted that African elephants (Loxodonta africana) would have similarly high visual acuity, necessary to facilitate eye-trunk coordination for feeding, drinking and social interactions. When tested on a discrimination task using Landolt-C stimuli, one African elephant cow demonstrated a visual acuity of 48′ of arc. This represents the ability to discriminate a gap as small as 2.75 cm in a stimulus 196 cm from the eye. This single-subject study provides a preliminary estimate of the visual acuity of African elephants

K Basins Groundwater Monitoring Task, K Basins Closure Project: Report for July, August, and September 2006

This report provides information on groundwater monitoring at the K Basins during July, August, and September 2006. Conditions remain very similar to those reported in the previous quarterly report, with no evidence in monitoring results to suggest groundwater impact from current loss of basin water to the ground. The K Basins monitoring network will be modified in the coming quarters as a consequence of remedial action at KE Basin, i.e., removal of sludge and basin demolition

K Basins Groundwater Monitoring Task, Spent Nuclear Fuels Project: Report for April, May, and June 2006

This report provides a summary of groundwater monitoring at the K Basins during April, May, and June 200

The effect of size and shape of targets upon the near lateral phoria and duction measurements

The problem was to determine the effect of size and shape of targets upon the near lateral phoria and duction measurements

School Vouchers: Settled Questions, Continuing Disputes

Provides an assessment of the constitutional principles announced by the Court, following the June 2002 decision in the Cleveland school voucher case. Presents contrasting arguments on educational policy that address key issues about the decision

Torts

Covers cases on violation of civil rights—damages (Peterson); on personal injuries as community property—res ipsa loquitur (Duggan); on defamation (Duggan); on storekeeper\u27s liability (Bader); on children staying after school—invitees or licensees (Bader); and on attractive nuisances (Brown)