PMC

Effect of modifying maltose, ascorbate, and hematocrit on glucose meter results. Solid lines represent line of equivalence (EQ); dashed lines represent estimated conditional mean values for glucose meters predicted from coefficients derived by linear regression. (A) Meter₁: (a) untreated, (b) 5.6 mmol/liter maltose, (c) 0.59 mmol/liter ascorbate, and (d) 5.6 mmol/liter maltose and 0.59 mmol/liter ascorbate. (B) Meter₂: (a) 0.59 mmol/liter ascorbate, (b) 5.6mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 43%, (c) 5.6mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 20%, and (d) 5.6 mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 55%. (C) Meter₃: (a) untreated overlaps with the solid line of equivalence, (b) 5.6 mmol/liter maltose, (c) 0.59 mmol/liter ascorbate, (d) 5.6 mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 43%, and (e) 5.6 mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 20%. (D) Meter₄: (a) untreated, (b) 5.6 mmol/liter maltose, (c) 0.59 mmol/liter ascorbate, (d) 5.6 mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 43%, and (e) 5.6 mmol/liter maltose, 0.59 mmol/liter ascorbate, and H = 20%.

Maltose binding pocket with maltose bound, surrounded by key residues. (a) Maltose binding pocket in the ATP state, maltose is represented in sticks and spheres, while the residues are portrayed in sticks only. (b) Maltose binding pocket in the ADP state, maltose is represented in sticks and spheres, while the residues are portrayed in sticks only. (c) Maltose binding pocket in the Apo state, represented in blue and green, respectively. The relevant aminoacids are represented in sticks, while maltose is represented in spheres and sticks.

(a). 2Fo-Fc electron density for maltose contoured at 1.5σ is shown. (b). Conformational changes upon binding of maltose. The structure of maltose bound MtbMaK (green color) was superimposed over the unliganded structure (blue color). Main and side chains of several residues move as a result of substrate binding. (c). Maltose binds in the C-lobe and is in proximity to the conserved motifs essential for catalysis. (d). A surface electrostatic potential representation of the region around the maltose binding site. Blue represents positive potential; red, negative potential. (e). Residues interacting with maltose. Residues from the catalytic loop interacting with maltose are shown as blue sticks, while P344 from the activation loop is shown as magenta sticks. Maltose is shown as sticks in panels A-E. (f). Alanine scanning mutagenesis of amino acids interacting with maltose. Relative activity of mutants (%) with respect to the wild type is plotted as a bar graph. Error bars represent s.d. (n = 3).

Reaction curves for the validation of the α- and β-maltose NADP-linked spectrophotometric assay. A, Sequential measurement of α- and β-maltose was achieved by adding maltose phosphorylase, then maltose epimerase to a reaction mixture that contained 650 pmol of commercially obtained maltose. B, β-Maltose produced by the action of β-amylase on 125 pmol maltoheptose (G7) was not acted on by maltose phosphorylase until maltose epimerase was added. A change in OD is observed only when maltose epimerase is added to the reaction mixture, demonstrating that maltose phosphorylase is specific for the α-anomer. In both A and B, Glc-6-P dehydrogenase and hexokinase were already added to the reaction mixture. MPL, Maltose phosphorylase; MER, maltose epimerase; β-Amy, β-amylase. Horizontal bar = 2 min in both A and B; vertical bar = 0.00092 OD units or 100 pmol under our assay conditions in both A and B.