In many photosynthetic organisms, tight-binding Rubisco inhibitors are released by the motor protein Rubisco activase (Rca). In higher plants, Rca plays a pivotal role in regulating CO₂ fixation. Here, the ATPase activity of 0.005 mm tobacco Rca was monitored under steady-state conditions, and global curve fitting was utilized to extract kinetic constants. The k_cat was best fit by 22.3 ± 4.9 min⁻¹, the K_m for ATP by 0.104 ± 0.024 mm, and the K_i for ADP by 0.037 ± 0.007 mm. Without ADP, the Hill coefficient for ATP hydrolysis was extracted to be 1.0 ± 0.1, indicating noncooperative behavior of homo-oligomeric Rca assemblies. However, the addition of ADP was shown to introduce positive cooperativity between two or more subunits (Hill coefficient 1.9 ± 0.2), allowing for regulation via the prevailing ATP/ADP ratio. ADP-mediated activation was not observed, although larger amounts led to competitive product inhibition of hydrolytic activity. The catalytic efficiency increased 8.4-fold upon cooperative binding of a second magnesium ion (Hill coefficient 2.5 ± 0.5), suggesting at least three conformational states (ATP-bound, ADP-bound, and empty) within assemblies containing an average of about six subunits. The addition of excess Rubisco (24:1, L8S8/Rca6) and crowding agents did not modify catalytic rates. However, high magnesium provided for thermal Rca stabilization. We propose that magnesium mediates the formation of closed hexameric toroids capable of high turnover rates and amenable to allosteric regulation. We suggest that in vivo, the Rca hydrolytic activity is tuned by fluctuating [Mg²⁺] in response to changes in available light.

In this issue, we offer a symposium‐in‐print that is focused on several new advancements in fundamental research related to the family of GFP (green fluorescent protein)‐like proteins. A few applied aspects are also included to illustrate the impact this amazing set of colored proteins has made on our understanding of cell biology at the molecular level. The six articles presented here cut across several disciplines ranging from biological function to protein structure to photophysical aspects. These highly original pieces of work include both experimental and computational approaches, and will provide the reader with significant insight into current, state‐of‐the‐art research activities in this very dynamic and fast‐paced field. In the first part of this perspective, I will give a brief overview of the history and salient features of GFPs, cite some examples that illustrate their impact on biotechnology, and provide a brief review of the structural and chemical features that lend these proteins their fascinating appearance. In the second part, I will introduce each of the peer‐reviewed contributions of the participating authors.