Absence or presence of van der Waals contact with Leu 596 for PEPCK polymorphic site Ile/Val 629. Models are of the lid-open conformation of the 5′-exon-excised mitochondrial form. Color codes as for Figures 6 and 7 except that Leu 596 is orange. Ile/Val 629 always makes van der Waals contact with Trp 595's β-CH2 group with some part of its side chain, but the part varies. a) allele SDI, no van der Waals contact between 596 and 629; b) allele SDV, strong van der Waals contact between 596 and 629. Small yellow numbers are distances between the indicated atoms in Å units.