Catalytic importance of a protonated adenosine in the hairpin ribozyme active site.

The hairpin ribozyme accelerates the rate of phosphodiester transfer reactions by at least 5 orders of magnitude. To achieve this rate enhancement, the active site forms via a substrate helix docking event that constrains the scissile phosphate linkage and positions G8 and A38 for catalysis, both of which have been implicated as sites of proton transfer in general acid-base catalysis. To investigate the functional groups required for hairpin activity, we previously reported a series of nucleotide analogue interference mapping experiments [Ryder, S.

Comparison of adaptations and compliance to exercise training between middle-aged and older men.

Objective: To compare the rate and magnitude of physiologic and psychologic adaptations to aerobic training between middle-age and older men, to assess their interest in continued participation (> 6 months) in a supervised high-intensity training program, and to evaluate the safety of high-intensity training for older people.

Design: Before-after intervention trial.

Setting: Medical center in a Midwestern metropolitan city.

Physiologic responses to shoveling and thermal stress in men with cardiac disease.

To investigate the effect of temperature stress on responses to static-dynamic work in patients with ischemic heart disease (IHD), 10 men with IHD shoveled gravel for 30 min in a warm (29 degrees C), neutral (24 degrees C), and cold (-8 degrees C) environment (on separate days). A pace of 15 lifts.min-1 was set, and the load per lift approximated 5.

Baltimore Therapeutic Equipment work simulator: energy expenditure of work activities in cardiac patients.

The energy expenditure and hemodynamic responses to tasks performed on the Baltimore Therapeutic Equipment (BTE) work simulator were evaluated in men with coronary artery disease and compared to tasks performed at a laboratory workstation in which actual tools and equipment were used. Met units for the BTE work simulator and corresponding workstation tasks, respectively, were drill press operation, 1.5 +/- 0.

Effect of age and coronary artery disease on response to snow shoveling.

Objectives: The objective of this study was to evaluate the effect of age and coronary artery disease on responses to snow shoveling.

Background: Little information is available on the hemodynamic and metabolic responses to snow shoveling.

Methods: Sixteen men with asymptomatic coronary artery disease and relatively good functional work capacity, 13 older normal men and 12 younger normal men shoveled snow at a self-paced rate.

Fluid-regulating hormones during exercise when central blood volume is increased by water immersion.

To examine the influence of an increase in central blood volume with head-out water immersion (WI) on fluid-regulating hormones during exercise, 10 healthy men underwent upright leg cycle exercise on land and with WI. Venous plasma renin activity and plasma venous concentrations of atrial natriuretic peptide, plasma aldosterone, and arginine vasopressin were determined at exercise intensities corresponding to approximately 40, 60, 80, and 100% peak oxygen consumption (VO2) and at minutes 1 and 5 of seated rest recovery within each environment. Peak VO2 did not differ on land and with WI.

Cardiovascular regulation during head-out water immersion exercise.

Head-out water immersion is known to increase cardiac filling pressure and volume in humans at rest. The purpose of the present study was to assess whether these alterations persist during dynamic exercise. Ten men performed upright cycling exercise on land and in water to the suprasternal notch at work loads corresponding to 40, 60, 80, and 100% maximal O2 consumption (VO2max).

Effect of increased central blood volume with water immersion on plasma catecholamines during exercise.

To examine the influence of an increase in central blood volume with head-out water immersion (WI) on the sympathoadrenal response to graded dynamic exercise, nine healthy men underwent upright leg cycle exercise on land and with WI. Plasma norepinephrine and epinephrine concentrations were used as indexes of overall sympathoadrenal activity. Oxygen consumption (VO2), heart rate, systolic blood pressure, and plasma concentrations of norepinephrine, epinephrine, and lactate were determined at work loads corresponding to approximately 40, 60, 80, and 100% peak VO2.

Weight carrying versus handgrip exercise testing in men with coronary artery disease.

The clinical merits of handgrip and weight carrying tests were compared in 30 patients with documented coronary artery disease. The static loads in the 2 tests were matched by percentage of maximal static effort and corresponded to 25 and 45% of maximal voluntary handgrip contraction and 25 and 45% of maximal 1-hand lift capacity. Each static load in both tests was continued for less than or equal to 3 minutes.