Miniature force sensor for absolute laser power measurements via radiation pressure at hundreds of watts.

We present a small power meter that detects the radiation pressure of an incident high-power laser. Given its small package and non-destructive interaction with the laser, this power meter is well suited to realizing a robust real-time, high-accuracy power measurement in laser-based manufacturing environments. The incident laser power is determined through interferometric measurement of displacement of a 20 mm diameter high reflectivity mirror, mounted at the center of a dual element spiral flexure. This device can measure laser power from 25 W to 400 W with a 260 m W/H z noise floor and ≤ 3.2% expanded uncertainty. We validate our device against a calibrated thermopile with simultaneous measurements of an unpolarized 1070 nm laser and report good agreement between the two systems. Finally, by referencing to an identical mechanical spring that does not see the incident laser, we suppress vibration noise in the power measurement by 14.8 dB over a 600 Hz measured bandwidth. This is an improvement over other radiation pressure based power meters that have previously been demonstrated.

A novel role for cytochrome c: Efficient catalysis of S-nitrosothiol formation.

Although S-nitrosothiols are regarded as important elements of many NO-dependent signal transduction pathways, the physiological mechanism of their formation remains elusive. Here, we demonstrate a novel mechanism by which cytochrome c may represent an efficient catalyst of S-nitrosation in vivo. In this mechanism, initial binding of glutathione to ferric cytochrome c is followed by reaction of NO with this complex, yielding ferrous cytochrome c and S-nitrosoglutathione (GSNO). We show that when submitochondrial particles or cell lysates are exposed to NO in the presence of cytochrome c, there is a robust formation of protein S-nitrosothiols. In the case of submitochondrial particles protein S-nitrosation is paralleled by an inhibition of mitochondrial complex I. These observations raise the possibility that cytochrome c is a mediator of S-nitrosation in biological systems, particularly during hypoxia, and that release of cytochrome c into the cytosol during apoptosis potentially releases a GSNO synthase activity that could modulate apoptotic signaling.

Nitrite reductase activity of cytochrome c.

Small increases in physiological nitrite concentrations have now been shown to mediate a number of biological responses, including hypoxic vasodilation, cytoprotection after ischemia/reperfusion, and regulation of gene and protein expression. Thus, while nitrite was until recently believed to be biologically inert, it is now recognized as a potentially important hypoxic signaling molecule and therapeutic agent. Nitrite mediates signaling through its reduction to nitric oxide, via reactions with several heme-containing proteins. In this report, we show for the first time that the mitochondrial electron carrier cytochrome c can also effectively reduce nitrite to NO. This nitrite reductase activity is highly regulated as it is dependent on pentacoordination of the heme iron in the protein and occurs under anoxic and acidic conditions. Further, we demonstrate that in the presence of nitrite, pentacoordinate cytochrome c generates bioavailable NO that is able to inhibit mitochondrial respiration. These data suggest an additional role for cytochrome c as a nitrite reductase that may play an important role in regulating mitochondrial function and contributing to hypoxic, redox, and apoptotic signaling within the cell.