Orthophosphate binding at the dimer interface of Corynebacterium callunae starch phosphorylase: mutational analysis of its role for activity and stability of the enzyme

Table 2 Comparison of half-life times (t_1/2) of recombinant wild-type Cc GlgP and site-directed enzyme variants in thermal denaturation experiments and in the presence of 0.4 M imidazole at 30°C

t _(1/2) [min]	inactivation at 45°C			inactivation by imidazole at 30°C
	no P_i	10.0 mM P_i	100 mM P_i	no P_i	5.0 mM P_i
wild-type	2.6	2.8 × 10²	3.5 × 10³	22	160
T28A	0.8	2.2	3.3 × 10²	1.9	5.6
K31A	5.3	1.7 × 10²	3.5 × 10³	10	25
S174A	2.8	33	9.9 × 10²	14	58
R141A	2.9	7.5	1.4 × 10³	6.4	27

The experiments were carried out in 50 mM triethanolamine buffer, pH 7.0. Values from linear regression analysis have S.D. of < 10%. Representative data were used for calculation of t_1/2.

ISSN: 1471-2091