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Biomedical subjects

O Lockridge

Publications and source records attributed to O Lockridge.

80 records · Page 5Linked to original sources
PubMed1977

Argininosuccinate synthetase activity in cultured human lymphocytes.

The activity of argininosuccinate synthetase (E.C. 6.3.4.5), a urea cycle enzyme, was measured in cultured human lymphocytes using a new radioactive assay. Control cells had a maximum specific activity of 15.7 +/- 8.7 nmoles per hour per milligram of protein and an apparent Km for citrulline of 2 X 10(-4) M, whereas cells derived from a patient with citrullinemia had no detectable activity. A nutritional variant, selected out of the citrullinemic lymphocyte population by ability to grow in citrulline, had a maximum specific activity of 10.7 +/- 3.8 nmoles/hr/mg and an apparent Km for citrulline of 2 X 10(-2) M. These measurements confirm the observation that citrullinemia is associated with a defect in argininosuccinate synthetase activity and provide further evidence that citrullinemia is expressed in cultured lymphocytes. The emergence of a nutritional variant with a partial defect in argininosuccinate synthetase enzyme suggests that this citrullinemic patient has a heterogeneous population of cells, some totally defective and others only partially defective in argininosuccinate synthetase. The new activity assay is described in detail.

Amino Acid Metabolism, Inborn Errors↗
PubMed1975

Citrulline metabolism in normal and citrullinemic human lymphocyte lines.

Citrullinemia is one of the five aminoacidurias associated with the Krebs-Henseleit urea cycle. A long-term lymphocyte line (UM-21) derived from a patient with this disease and nine of ten clones of this line were found to have no activity for the enzyme argininosuccinate synthetase (AS), as demonstrated by their inability to grow in medium in which citrulline had been substituted for arginine, by their inability to incorporate arginine-C14 derived from citrulline-C14 into cellular protein, and by direct enzyme assay. One clone had normal or nearly normal argininosuccinate synthetase activity, as demonstrated by the same criteria. Nutritional "variants" able to grow logarithmically in medium containing citrulline were isolated from UM-21 and three clones. The apparent Kms of AS for citrulline in UM-21, the ten clones, the variant lines, and a normal line were measured and fell into three groups: AS in UM-21 and nine clones had no measurable apparent Km for citrulline; AS in the variant cells had apparent Kms for citrulline of approximately 20 mM; and AS in the normal cell line and one clone had apparent Kms for citrulline of 0.2 mM. The data suggest that the defect in the citrullinemic cell lines is due to a mutation in the structural gene coding for argininosuccinate synthetase.

Amino Acid Metabolism, Inborn Errors↗
PubMedDate not supplied

Enzymes hydrolyzing organophosphates as potential catalytic scavengers against organophosphate poisoning.

Enzymes hydrolyzing organophosphates could be used as catalytic scavengers for treatment of organophosphate poisoning and for decontamination. Two organophosphorus hydrolases (OPH) were selected: the Flavobacterium sp/Pseudomonas diminuta phosphotriesterase (PTE) and human paraoxonase (HuPON). Genes encoding these enzymes were cloned and functional recombinant enzymes expressed. PTE was expressed in E. coli. Natural HuPON was purified from human plasma; recombinant HuPON was expressed in human embryonic kidney 293 T cells. Although HuPON displays interesting catalytic properties, a site-directed mutagenesis program was undertaken to improve its catalytic efficiency. PTE has high efficiency in hydrolysis of organophosphates, including nerve agents. PTE injected in rat has a half-life of 100 min. However, to overcome pharmacokinetic problems of injected OPH and/or immunological incompatibility, the model enzyme (recombinant PTE) was immobilized onto a hollow-fiber reactor. This reactor designed for extracorporeal blood circulation is under experimentation for post-exposure detoxification.

Animals↗
PubMedDate not supplied

Pesticides and susceptible populations: people with butyrylcholinesterase genetic variants may be at risk.

Butyrylcholinesterase (BChE) scavenges low doses of organophosphorus (for example, paraoxon) and carbamate pesticides (for example, carbaryl) and in this way protects people from the toxic effects of these poisons. The protective role of BChE is demonstrated by the finding that pesticide applicators can have reduced BChE activity with no clinical signs of poisoning. The question has arisen whether people with genetic variants of BChE are less protected. Seventy-six percent of the population is homozygous for wild-type BChE, while 24% carry at least one genetic variant allele. Most genetic variants of BChE have reduced activity. The clinically most important variant is atypical (D70G) BChE because people with this variant have 2 hours of apnea after receiving a dose of succinylcholine that is intended to paralyze muscles for 3-5 minutes. In test tube experiments the atypical variant reacts more slowly with all positively charged compounds (for example physostigmine, echothiophate). This leaves more toxin available for reaction with acetylcholinesterase in nerve synapses and predicts that people with atypical BChE will be less protected. Variants with low activity, such as silent BChE, are predicted to be at increased risk from organophosphorus pesticides based on experiments in monkeys and rodents where injection of purified BChE protected animals from the toxic effects of nerve agents. More studies are needed to strengthen the hypothesis that people with genetic variants of BChE are at higher risk of intoxication from pesticides.

Animals↗