Table 3

Recombinant human HNMT substrate kinetics and thermal inactivation

AlleleKmT50
HistamineAdo-MetStandard assayModified assay
μm degrees
HNMT*1A 25.3  ± 0.2510.0  ± 0.2157.2  ± 0.1355.9  ± 0.03
HNMT*1B 23.4  ± 0.288.2  ± 0.1456.9  ± 0.0356.1  ± 0.03
HNMT*2A 35.0  ± 2.0711.7  ± 1.0554.6  ± 0.1052.3  ± 0.30
HNMT*2B 35.5  ± 1.5513.0  ± 0.5254.2  ± 0.2650.9  ± 0.46

Apparent K m values and temperatures resulting in 50% inactivation after a 15-min preincubation (T50) are listed.

    • All values are mean ± standard error for three determinations.

    • K m values for histamine for both of the proteins encoded by *1 constructs were significantly different from those encoded by *2 constructs (p < 0.01 by ANOVA).

    • T50 values for proteins encoded by *1 constructs differed significantly from those for proteins encoded by *2constructs (p < 0.01 by ANOVA).

    • Please see text for an explanation of the “standard” and “modified” assays.