Adenosine triphosphate (ATP) drives many critical cellular processes. We have used laser-induced release from a caged, inactive form of ATP (NPE-caged) followed by short X-ray pulses at the dedicated time-resolved X-ray solution scattering (TR-XSS) beamline ID09 at ESRF-EBS to study protein conformational change in real time. Because the NPE-caged ATP releases on a millisecond timescale, our studies have so far been blind to sub-millisecond structural intermediates. We now propose to use a different chemistry of the caged ATP (pHP-caged) that releases ATP in nanoseconds. We will track sub-millisecond domain movements and kinetics in calcium transport (skeletal-muscle SERCA1a and bacterial LMCA1) and in enzymatic energy conversion by adenylate kinase. The results will enable characterization of the faster events not characterized in solution for these proteins, can potentially revise earlier observations, and set a novel standard for TR-XSS experiments with caged compounds.