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Biomedical subjects

D Steinberg

Publications and source records attributed to D Steinberg.

At least 361 records · Page 20Linked to original sources
PubMed1967

Refsum's disease: nature of the enzyme defect.

Two siblings with Refsum's disease, an inherited disorder of lipid metabolism, oxidized intravenously injected uniformly labeled phytanic acid-C(14) at rates less than 5 percent of those found in normal subjects. The defect in oxidation of phytanic acid persisted in cultures of fibroblasts from the patients' skin. The rate of oxidation of the phytanic acid-C(14) was less than 1 percent of that found in cultures of fibroblasts from normal skin. However, pristanic acid, previously shown to be the first product of phytanic acid degradation, was oxidized at a normal rate in the patients' cultures. These results indicate that the enzymatic defect in Refsum's disease is in the first step of the pathway for degradation of phytanic acid, that is, in the unusual alpha-oxidative process that leads to a shortening of phytanic acid by one carbon atom.

Carbon Dioxide↗
PubMed1967

Studies on the metabolic error in Refsum's disease.

Studies utilizing mevalonic acid-2-(14)C and D(2)O as precursors failed to provide evidence for an appreciable rate of endogenous biosynthesis of phytanic acid in a patient with Refsum's disease. Orally administered tracer doses of phytol-U-(14)C were well absorbed both by seven normal control subjects (61 to 94%) and by two patients with Refsum's disease (74 and 80%). The fraction of the absorbed dose converted to (14)CO(2) in 12 hours was 3.5 and 5.8% in Refsum's disease patients and averaged 20.9% in seven control subjects. Labeled phytanic acid was demonstrated in the plasma of both control subjects and patients given phytol-U-(14)C, establishing phytol in the diet as a potential precursor of phytanic acid. This labeled phytanic acid had disappeared almost completely from the plasma of the seven control subjects by 24 to 48 hours, whereas it persisted at high concentrations in the plasma of the two patients for many days. We conclude that the phytanic acid accumulating in Refsum's disease is primarily of exogenous origin and that patients with Refsum's disease have a relative block in the degradation of phytanic acid and possibly other similar branched-chain compounds. This may relate to a deficiency in mechanisms for release of phytanic acid from stored ester forms or, more probably, to reactions essential to oxidative degradation of the carbon skeleton.

Adult↗
PubMed1967

Absorption of phytol from dietary chlorophyll in the rat.

The fate of ingested chlorophyll-particularly of the phytol portion of the molecule-was studied. Uniformly (14)C-labeled pheophytin a (the Mg-free derivative of chlorophyll a) was prepared from an extract of tobacco leaves grown in (14)CO(2), and was administered by stomach tube to rats in which the thoracic duct had been cannulated. Only about 2% of the administered radioactivity was absorbed in 24 hr, largely into the thoracic duct lymph. Moreover, only a fraction of this lymph radioactivity was derived from phytol (i.e., was found in phytol, phytenic acid, or phytanic acid). The results indicated that not more than 1-2% of chlorophyll phytol is available for absorption by the rat. Similarly, after the administration of whole spinach or spinach extract (not labeled) to rats, only about 1% of the total phytol content was absorbed into the intestinal lymph. Nearly all of the administered phytol was found in the feces and the contents of the colon, and was still largely in the form of pheophytin. The study also indicated that little of the nonphytol portion of the chlorophyll molecule is absorbed.

Animal Nutritional Physiological Phenomena↗