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Biomedical subjects

K J Scully

Publications and source records attributed to K J Scully.

10 recordsLinked to original sources
PubMed1979

Human propionyl CoA carboxylase: some properties of the partially purified enzyme in fibroblasts from controls and patients with propionic acidemia.

We report some properties of propionyl CoA carboxylase (PCC) partially purified from cultured human fibroblasts obtained from controls and several patients with propionic acidemia. A series of steps (Triton X-100 treatment, high speed centrifugation, ammonium sulfate precipitation, and density gradient centrifugation) led to 100- to 300-fold purification of control enzyme. Control PCC had a molecular weight of nearly 700,000, contained biotin, demonstrated a pH optinum at 8.0-8.5, was activated by potassium, and followed Michaelis-Menten kinetics for each of its substrates. It was distinguished from acetyl CoA carboxylase immunologically as well as by differential purification. Each of seven lines from patients with propionic acidemia had clearly detectable PCC activity which was less than 5% of that in control lines. Although yields were poor and purification less extensive than in control lines, mutant PCC was enriched 2- to 40-fold by the same procedures employed for the control enzyme. Mutant enzyme had a pH optimum, ionic requirements, and substrate Km's similar to those of control PCC, but was distinctly more labile to both cold and heat. These findings suggest that the markedly reduced activity of PCC in these patients results from a mutation in the PCC structural gene locus or loci which leads to the synthesis of altered enzyme protein molecules.

Adult↗
PubMed1977

Genetic complementation of propionyl-CoA carboxylase deficiency in cultured human fibroblasts.

Propionyl-CoA carboxylase (PCC) deficiency is an inherited metabolic disorder showing considerable variability of expression. We have investigated the possibility that there is a genetic basis for the clinical heterogeneity in this disorder by examining complementation in Sendai virus mediated heterokaryons of mutant fibroblast strains. Restoration of PCC activity was monitored in individual multinucleate cells in situ using a radioautographic procedure which detects the incorporation of 14C-propionate into trichloracetic acid precipitable material. Each mutant strain incorporated negligible amounts of radioactivity compared to control strains. Activity was not restored when different mutants were mixed without virus or when homokaryons were produced by self-fusion. Seven mutant strains were fused in all pairwise combinations and examined for increased 14C-propionate incorporation in heterokaryons. Two main complementation groups were revealed. One group was composed of three mutants. The other was a complex group composed of four mutants in which intragroup complementation was demonstrated. Two mutants showing excellent complementation by radioautography were examined for complementation by the direct assay of PCC ACTIVITY. The enzyme activity of virus-treated preparations with 23% multinucleate cells was 183 U (pmol/min/mg protein) compared to 16 U for the untreated mixture (normal range 450-850 u). We conclude that PCC deficiency resulted from mutations of heterogeneous origin, although the classification of mutants into complementation groups did not correlate with patterns of clinical heterogeneity.

Amino Acid Metabolism, Inborn Errors↗
PubMed1976

Defective leukocyte metabolism in human cobalamin deficiency: impaired propionate oxidation and serine biosynthesis reversible by cyanocobalamin therapy.

Biochemical disturbances common to vitamin B12 and folate deficiency were investigated in leukocytes from patients with cobalamin deficiency. The investigations focused on the only two human metabolic pathways known to require vitamin B12. In the propionate pathway, deoxyadenosylcobalamin is required for isomerization of methylmalonyl-CoA to succinyl-CoA. Leukocyte oxidation of 14C-propionate to 14CO2 was markedly decreased in 9 patients with Addisonian cobalamin deficiency and 2 patients with low serum cobalamin associated with folate deficiency, whereas 14C-succinate oxidation was normal. Three of the Addisonian patients had only minimal anemia. Within 4 days after one injection of 1,000 mug of cyanocobalamin, in 7 out of 8 patients studied, leukocyte propionate oxidation increased to normal levels. In folate-mediated one-carbon metabolism, as measured by serine biosynthesis from formate, methylcobalamin is required for conversion of methyl-folate to tetrahydrofolate. Leukocyte formation of 14C-serine from 14C-formate was significantly depressed in 5 patients with low serum cobalamin, little or no anemia, and only marginally low total red cell folate, the low serum cobalamin in 2 of these patients was associated with folate deficiency. After 1,000 mug of cyanocobalamin, in 2 of 3 patients, leukocyte serine biosynthesis increased to the normal range. These observations demonstrated that these two metabolic pathways in leukocytes were sensitive to cobalamin deficiency, and responsive to cobalamin therapy. Although there was no correlation between either of these metabolic activities and the serum cobalamin, red cell folate, or hematocrit, there was a striking correlation between impairment of leukocyte propionate oxidation and of leukocyte serine biosynthesis in 5 patients who were minimally anemic. The remarkably close correspondence between effects of low cobalamin on these two metabolic pathways, in nonanemic patients, must be a direct consequence of their common requirements for a cobalamin co-enzyme. These findings emphasize the importance of cobalamin in folate metabolism, and are consistent with the hypothesis that folate is "trapped" as methyl-folate in cobalamin deficiency, but do not exclude the possibility that this "trapping" is caused by a third metabolic function of cobalamin which might mediate transport of folate into cells.

Adult↗
PubMed1971

Inherited propionyl-Coa carboxylase deficiency in "ketotic hyperglycinemia".

Cultured fibroblasts from a young girl with ketotic hyperglycinemia were unable to oxidize propionate-(14)C to (14)CO(2), but oxidized methylmalonate-(14)C and succinate-(14)C normally. This block in propionate catabolism was shown to result from a lack of propionyl-CoA carboxylase activity. The carboxylase deficiency was not due to the presence of an intracellular inhibitor and it was not corrected by biotin, a known cofactor for the enzyme. Both of her parents' fibroblasts had approximately 50% of normal propionyl-CoA carboxylase activity. These results demonstrate that ketotic hyperglycinemia and propionicacidemia are the same disease, caused by a mutation of the propionyl-CoA carboxylase apoenzyme, which is inherited as an autosomal recessive trait. This enzymatic localization provides an explanation for the remarkable clinical and chemical similarity between ketotic hyperglycinemia and methylmalonicaciduria and offers a potential means of antenatal detection of this disorder.

Acidosis↗