Table 1. KIEs in Ras-catalyzed GTP hydrolysis.

Isotopomer	No. of determinations	18(V/K) (average)	18(V/K)*
Control†	8	1.0026 (0.0028)	1.0026
[γ18O3]GTP	10	1.0012 (0.0026)	1.0013
[γ18O4]GTP	9	1.0121 (0.0019)	1.0129
[β18O3]GTP	8	1.0186 (0.0025)	1.0194
[β18O2]GTP	6	1.0099 (0.0016)	1.0105
β-γ bridge‡			1.0116
β-γ bridge§			1.0088

^*Corrected for incomplete ¹⁸O labeling.

^†Substrate consists of ¹³C-depleted GTP and GTP containing ¹³C but not ¹⁸O labels.

^‡Calculated as the ratio of ¹⁸(V/K)s in [γ¹⁸O₄]GTP and [γ¹⁸O₃]GTP.

^§Calculated as the ratio of ¹⁸(V/K)s in [β¹⁸O₃]GTP and [β¹⁸O₂]GTP.