Figure 1. Diagram of experimental apparatus.

A, laser diffractometer. The beam from a 5 mW HeNe laser was passed through shaping (RL1) and Fraunhofer (RL2) lenses (see text) via a mirror that adjusted the angle of incidence onto the fibre. The fibre was mounted horizontally in a small drop of solution (8 or 40 μl) between a glass pedestal and a glass coverslip by hooks attached to a servomotor and force transducer (not shown). The zeroth-order beam was blocked by a movable mask, whilst the first-order beam was focused onto a position-sensitive photodiode by a third cylindrical lens (RL3). Additional masks at the photodiode blocked scattered and unwanted diffracted light. The fibre was positioned ∼110 mm from the photodiode. Drawing not to scale. B, uncaging beam and temperature control. The pulse from the ultraviolet (UV) laser passed horizontally through the fibre and was shaped by an orthogonal pair of cylindrical quartz lenses (UL1 and UL2) to match the front face of the uncaging chamber (∼4 mm × 2 mm). The front face of the uncaging chamber was made of quartz; the rear face was a no. 3 glass coverslip mirrored on its rear face to increase the UV illumination of the caged ATP. The uncaging chamber was mounted on a rotating platform that contained four additional pedestals in a pentagonal array holding 40 μl drops of pre-activating or non-caged-ATP-activating solutions (see text). Lenses represented as rectangles indicate cylindrical lenses with their axes in the plane of the page. A UV-blocking filter (UVF) prevented scattered UV light from reaching the position-sensitive photodiode.