I present a theoretical model of the Nd1-H-Od1 hydrogen bond in low-pH alpha-chymotrypsin and alpha-lytic protease that reproduces the experimentally observed proton chemical shift and H/D fractionation factor. The validated model is used to predict additional properties for this hydrogen bond (the NH bond length, the proton-tritium chemical shift difference, and ratio of proton/deuterium stretching frequencies) that are consistent with experimental values obtained for related systems.