Table III.

Effect of nucleotide on the temperature sensitivity of the ATPase activity of recombinant Rubisco activase

Enzyme	T50
	No nucleotide	2 mm ADP	2 mm ATP-γ-S
43-kD RWT	31	43.5	43.5
Q111D	29.5	39	46
Q111E	30	42.5	46
46-kD RWT	32.5	44.5	43.5

Temperature treatments in the presence or absence of nucleotide and the spectrophotometric assay of ATPase activity are described in “Materials and Methods.” The 43- and 46-kD RWT enzymes are the small and large recombinant Arabidopsis isoforms. Q111D and Q111E are the recombinant 43-kD isoforms with Glu and Asp substitutions, respectively, at position 111. T₅₀ is the calculated temperature in °C for 50% reduction in activity after treatment.