Biochemical Characterization of a Partial Deficiency for Ump Synthase in Holstein Cattle (Enzyme, Genetic Disorder, Metabolic Defect, Hereditary Orotic Aciduria)
Harden, Kathryn Knosher
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https://hdl.handle.net/2142/77457
Description
Title
Biochemical Characterization of a Partial Deficiency for Ump Synthase in Holstein Cattle (Enzyme, Genetic Disorder, Metabolic Defect, Hereditary Orotic Aciduria)
Author(s)
Harden, Kathryn Knosher
Issue Date
1986
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Animal Pathology
Language
eng
Abstract
A partial deficiency for uridine-5'-monophosphate (UMP) synthase in Holstein cattle was characterized biochemically. Activity is half normal in animals that are heterozygous for a potentially lethal gene. Hemolysates were used as the source of enzyme for these studies after verifying that the deficiency is generalized to all tissues. The protein product of the mutant allele for UMP synthase was shown to be present in hemolysates of heterozygotes by immunotitration of enzyme activity. The activities comprising UMP synthase, orotate phosphoribosyltransferase (OPRT) and orotidine-5'-monophosphate (OMP) decarboxylase (ODC) were measured separately. ODC activity was about 47% of normal in heterozygotes, comparable to the reduction in UMP synthase. In contrast, OPRT was reduced to only 63%. In intact erythrocytes, UMP synthase activity was reduced relative to hemolysates, and the enzyme deficiency in heterozygotes was undetectable. Biochemical tests were conducted to assess whether the mutant UMP synthase had measurable activity when assay conditions were altered or if its presence affected the normal enzyme under these conditions. Kinetic constants for orotic acid (OA), phosphoribosylpyrophosphate (PRPP), and OMP were comparable in the two groups. UMP synthase from both responded similarly to inhibition by 5-fluoroorotate, inorganic pyrophosphate, and 6-azaUMP. An endogenous inhibitor was not present in hemolysates from heterozygotes. Response to pH was comparable in the two groups. Thermal inactivation of UMP synthase did not distinguish heterozygotes from controls nor did a test of the stability of UMP synthase when hemolysates were stored at 4(DEGREES). Other parameters relating to nucleotide metabolism did not differ between the groups, including concentration of PRPP and activities of PRPP synthetase, adenine phosphoribosyltransferase, and hypoxanthine-guanine phosphoribosyltransferase. Urinary OA concentration during the first six weeks of life was similar in calves normal and heterozygous for UMP synthase. Four cows, including one heterozygote (4837), were injected for ten days with growth hormone. None of the treated cows exhibited changes in erythrocyte UMP synthase activity, milk OA, or urinary OA. The increase in milk production in cow 4837 was much less than the mean of the other three treated animals but whether this was due to her partial deficiency for UMP synthase could not be determined.
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