Electron Transfer Precedes ATP Hydrolysis during Nitrogenase Catalysis

The biological reduction of N2 to NH3 catalyzed by Mo-dependent nitrogenase requires at least eight rounds of a complex cycle of events associated with ATP-driven electron transfer (ET) from the Fe protein to the catalytic MoFe protein, with each ET coupled to the hydrolysis of two ATP molecules. Although steps within this cycle have been studied for decades, the nature of the coupling between ATP hydrolysis and ET, in particular the order of ET and ATP hydrolysis, has been elusive. Here, we have measured first-order rate constants for each key step in the reaction sequence, including direct measurement of the ATP hydrolysis rate constant: kATP = 70 s−1, 25 °C. Comparison of the rate constants establishes that the reaction sequence involves four sequential steps: (i) conformationally gated ET (kET = 140 s−1, 25 °C), (ii) ATP hydrolysis (kATP = 70 s−1, 25 °C), (iii) Phosphate release (kPi = 16 s−1, 25 °C), and (iv) Fe protein dissociation from the MoFe protein (kdiss = 6 s−1, 25 °C). These findings allow completion of the thermodynamic cycle undergone by the Fe protein, showing that the energy of ATP binding and protein–protein association drive ET, with subsequent ATP hydrolysis and Pi release causing dissociation of the complex between the Feox(ADP)2 protein and the reduced MoFe protein

Systems, Methods and Apparatus for Position Sensor Digital Conditioning Electronics

Systems, methods and apparatus are provided through which in some implementations determine the amplitude of an amplitude modulated signal, modulated by the position of an object being sensed. In some aspects, the apparatus accepts an excitation signal and the amplitude modulated signal and divides the amplitude modulated by the excitation signal to produce an output signal that is proportional to the position of the object being sensed. In other aspects, the division is performed only when the excitation signal is non-zero, such as close to the peaks in the excitation signal. In other aspects, the excitation signal and amplitude modulated signal are degraded due to an air gap and the degraded signals are used to correct for amplitude fluctuations due to the air gap, and produce an output signal, tolerant of the air gaps, that is proportional to the position of the object being sensed

Reconfigurable Drive Current System

A reconfigurable drive current system includes drive stages, each of which includes a high-side transistor and a low-side transistor in a totem pole configuration. A current monitor is coupled to an output of each drive stage. Input channels are provided to receive input signals. A processor is coupled to the input channels and to each current monitor for generating at least one drive signal using at least one of the input signals and current measured by at least one of the current monitors. A pulse width modulation generator is coupled to the processor and each drive stage for varying the drive signals as a function of time prior to being supplied to at least one of the drive stages

Motor Controller System For Large Dynamic Range of Motor Operation

A motor controller system uses a rotary sensor with a plurality of signal conditioning units, coupled to the rotary sensor. Each of these units, which is associated with a particular range of motor output shaft rotation rates, generate a feedback signal indicative of the position of the motor s output shaft. A controller (i) converts a selected motor output shaft rotation rate to a corresponding incremental amount of rotational movement for a selected fixed time period, (ii) selects, at periodic completions of the selected fixed time period, the feedback signal from one of the signal conditioning units for which the particular range of motor output shaft rotation rates associated therewith encompasses the selected motor output shaft rotation rate, and (iii) generates a motor drive signal based on a difference between the incremental amount of rotational movement and the feedback signal from the selected one of the signal conditioning Units

Eutrophication Assessment of Mt. Dell Reservoir

The degree and possible causes of eutrophication in Mt. Dell Reservoir, a small water supply reservoir in Parleys Canyon above Salt Lake City, were examined with a number of limnological studes. These studies described external (incoming stream flow) and internal (sediment) nutrient sources, general limnology, nutrient limitations, and trophic state. A monthly program of sampling at selected stream sites determined taht one area of mixed agricultural and undistrubed rangeland contributed significant amounts of total soluble inorganic nitrogen. Sediment phosphorus uptake and release rates were determined with aquatic three-phase microcosms. The results indicated that sediment phosphorus mass loadings were small (less than 5% of the total loading) compared to stream phosphorus mass loadings if the hypolimnion is aerobic. Anoxic conditions could cause sediment phosphorus releases to be greater than stream phosphorus mass loadings (about 68% of the total). Descriptive limnologies indicated that the reservoir was alkaline (pH about 8.0 and alkalinities usually around 200 mg CaCO3.a), dimictic, weakly stratified, and usually well oxygenated. Nutrient levels were usually highest during the winter and at greater depths. Highest total phosphorus and orthophosphate levels were generally within a range of 50-100 ug/l whereas total nitrogen and total soluble inorganic nitrogen concentrations ranged from 0.1 to 2.0 mg/l. Blue-green algae were the dominant algal type comprising 80 percent of the total algal composition. Algae were most numerous and chlorophyl