Cuticular Ridge Pattern in \u3ci\u3eOstertagia gruehneri\u3c/i\u3e and \u3ci\u3eOstertagia arctica\u3c/i\u3e (Nematoda: Trichostrongyloidea) from Caribou, \u3ci\u3eRangifer tarandus\u3c/i\u3e

Two species of medium stomach worms are common parasites of the caribou, Rangifer tarandus. The two species, Ostertagia gruehneri Skrjabin, 1929, and O. arctica Mitzkewitzsch, 1929, differ so markedly in morphology of the spicules and genital cone that many nematode systematists place them in different genera. Recent studies of similar pairs of species parasitic in other ruminants have provided evidence that such pairs of species may be morphotypes of one species. The two species from caribou are redescribed with emphasis on the pattern of surface cuticular ridges and the structure of the esophagus, characters considered useful for distinguishing species of trichostrongyloid nematodes. Ostertagia gruehneri and O. arctica were found to have identical ridge patterns and esophageal characteristics. Both species had five lateral ridges, a long eosphageal valve, and ducts for the subventral esophageal glands that opened internally posterior to the level of the cervical papillae

Conformational Plasticity and Structure/Function Relationships in Cytochromes P450

The cytochrome P450s are a superfamily of enzymes that are found in all kingdoms of living organisms, and typically catalyze the oxidative addition of atomic oxygen to an unactivated C-C or C-H bond. Over 8000 nonredundant sequences of putative and confirmed P450 enzymes have been identified, but three-dimensional structures have been determined for only a small fraction of these. While all P450 enzymes for which structures have been determined share a common global fold, the flexibility and modularity of structure around the active site account for the ability of P450 enzymes to accommodate a vast number of structurally dissimilar substrates and support a wide range of selective oxidations. In this review, known P450 structures are compared, and some structural criteria for prediction of substrate selectivity and reaction type are suggested. The importance of dynamic processes such as redox-dependent and effector-induced conformational changes in determining catalytic competence and regio- and stereoselectivity is discussed, and noncrystallographic methods for characterizing P450 structures and dynamics, in particular, mass spectrometry and nuclear magnetic resonance spectroscopy are reviewed. Antioxid. Redox Signal. 13, 1273–1296