FIGURE 2.
3-PGK as a source of ATP. (A) The three-dimensional crystal structure of yeast 3-PGK is outlined in shading, together with the projection of its products Mg-ATP (solid) and 3-phosphoglycerate (hatched), modified from Watson et al. (18). Note that the bulky structure of the enzyme provides a lower limit for the size of the ATP source. (B) A hypothetical cluster of all 3-PGK copies contained in an astrocyte would occupy a sphere of ∼100 nm diameter. The lack of domain generation by either arrangement is discussed in the text.