title: The kinetic properties of the glutamate dehydrogenase of Teladorsagia circumcincta and their significance for the lifestyle of the parasite.
abstract: Like other nematodes, both L(3) and adult Teladosagia circumcincta secrete or excrete NH(3)/NH(4)(+), but the reactions involved in the production are unclear. Glutamate dehydrogenase is a significant source NH(3)/NH(4)(+) in some species, but previous reports indicate that the enzyme is absent from L(3)Haemonchus contortus. We show that glutamate dehydrogenase was active in both L(3) and adult T. circumcincta. The apparent K(m)s of the L(3) enzyme differed from those of the adult enzyme, the most significant of these being the increase in the K(m) for NH(4)(+) from 18mM in L(3) to 49mM in adults. The apparent V(max) of the oxidative deamination reaction was greater than that of the reductive reaction in L(3), but this was reversed in adults. The activity of the oxidative reaction of the L(3) enzyme was not affected by adenine nucleotides, but that of the reductive reaction was stimulated significantly by either ADP or ATP. The L(3) enzyme was more active with NAD(+) than it was with NADP(+), although the activities supported by NADH and NADPH were similar at saturating concentrations. While the activity of the oxidative reaction was sufficient to account for the NH(3)/NH(4)(+) efflux we have previously reported, the reductive amination reaction was likely to be more active.
authors.affiliation: Faculty of Medicine and Health Sciences, Universiti Malaysia Sarawak, Malaysia.
authors.forename: Noorzaid
authors.initials: N
authors.lastname: Muhamad
authors.forename: David C
authors.initials: DC
authors.lastname: Simcock
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Pedley
authors.forename: Heather V
authors.initials: HV
authors.lastname: Simpson
authors.forename: Simon
authors.initials: S
authors.lastname: Brown
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D003641:Deamination; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D006189:Haemonchus / Q000201:enzymology; D007700:Kinetics; D007814:Larva / Q000201:enzymology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010028:Ostertagia / Q000201:enzymology*; D010029:Ostertagiasis / Q000201:enzymology / Q000469:parasitology; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D009243:NAD; D009249:NADP; D000244:Adenosine Diphosphate; D000641:Ammonia; D000255:Adenosine Triphosphate; D005969:Glutamate Dehydrogenase