When Chapman et al. (1999) were determining the 5MDH structure of malate dehydrogenase, they provided the enzyme with tetrahydroNAD Links to an external site. instead of the closely-related endogenous substrate NAD+ Links to an external site. . They also provided alpha-ketomalonate Links to an external site. instead of the endogenous substrate malate Links to an external site. .    The authors said that they had to use this approach because "stable ternary complexes suitable for crystallographic analysis are hard to devise" and that either one or both of the substrates would need to be an analog.   This enzyme typically oxidizes a 4-carbon skeleton (malate), and they looked for suitable analogs. They noted that "alpha-ketomalonate is chemically stable, binds with reasonable affinity (Km = 1.0 mM) and is efficiently reduced... (kcat = 300 s -1)."   What would 'poor' Km and kcat values have looked like in a 'highly disappointing' candidate? Think back to previous lab coverage on this topic (3A, 4A). What were they looking for when making these comparisons? Which direction is 'impressive' for each of these two enzyme descriptors?   To avoid a disappointing result they wanted to make sure that the alpha-ketomalonate Km was fairly ______ and the kcat was fairly ______ in order to reasonably mimic a natural substrate like malate.