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Biomedical subjects

P R Borum

Publications and source records attributed to P R Borum.

44 records · Page 3Linked to original sources
PubMed1979

Carnitine content of liquid formulas and special diets.

Radioisotopic analyses for carnitine content were done on infant formula, formulas for tube feeding, food supplements, and chemically defined diets. The carnitine content of the diets depend on the protein source. Products whose main protein source is soy protein isolate, casein, or egg white solids contain 4 nmole carnitine per milliliter or less, with most of them containing undetectable amounts of carnitine. Products based on milk or beef contain 50 to 656 nmole carnitine per milliliter. The daily requirement of the body for carnitine is unknown. Evidence is discussed that indicates that the possible use of carnitine as a supplement to formula diets intended for long-term care needs to be considered.

Animals↗
PubMed1978

Variation in tissue carnitine concentrations with age and sex in the rat.

Diabetes, starvation and various hormonal treatments are known to alter drastically carnitine concentrations in the body. Before the mechanisms controlling carnitine metabolism could be determined, it was necessary to establish normal carnitine concentrations in both sexes at different ages. Carnitine was assayed in plasma, liver, heart and skeletal muscle of rats from birth to weaning. The plasma carnitine increased rapidly during the first 2 days after birth. Carnitine in both heart and skeletal muscle increased, whereas liver concentrations declined during the first week of life. A carnitine-free diet containing sufficient precursors for carnitine biosynthesis was fed to weanling rats. Groups of ten male and ten female rats were killed each week for 10 consecutive weeks. Carnitine was determined in plasma, liver, heart, skeletal muscle, urine and epididymis in the male. There was no difference in carnitine concentrations between the sexes at weaning. Plasma, heart and muscle concentrations were higher in adult male rats than in adult females. However, liver carnitine and urinary carnitine concentrations were higher in adult female than in adult male rats. The epididymal carnitine concentration increased very rapidly during 50 to 70 days of age and the differences in carnitine concentrations between the sexes also became apparent during this time. Thus both the age and the sex of the human subject or experimental animal must be considered when investigating carnitine metabolism.

Age Factors↗
PubMed1978

Altered tissue carnitine levels in animals with hereditary muscular dystrophy.

Low levels of muscle carnitine have been found in patients with Duchenne dystrophy, a case possibly of Becker dystrophy, and limb-girdle syndrome as well as in patients with the recently described muscle carnitine deficiency syndrome. Tissues of the mouse, hamster, and chicken were analyzed to determine whether tissue carnitine levels were altered in the animal models of muscular dystrophy. Significantly higher levels of carnitine were found in dystrophic mouse muscle, but carnitine levels in plasma, liver and heart were normal. Histological changes in the skeletal muscle of dystrophic hamsters were relatively mild, and both skeletal muscle and plasma levels were normal. The liver carnitine level was higher than normal levels. The dystrophic hamster also had an inherited cardiomyopathy, and interestingly its heart carnitine level was much lower than normal. The red muscle of the normal chicken contained 5 times the level of carnitine found in white muscle. The dystrophic chicken had higher than normal levels of carnitine in the white muscle, but normal levels in the red muscle. Although all 3 animal models of muscular dystrophy studied have altered levels of carnitine in some tissue, none of the animal models had the same pattern of altered tissue carnitine levels seen in human patients.

Animals↗
PubMed1977

Purification of S-adenosylmethionine: epsilon-N-L-lysine methyltransferase. The first enzyme in carnitine biosynthesis.

The initial steps of carnitine biosynthesis in Neurospora crassa involve the methylation of the epsilon-amino group of lysine as follows: Lysine A leads to monomethyllysine B leads to dimethyllysine C leads to trimethyllysine. The methyl donor is S-adenosylmethionine. An enzyme, S-adenosylmethionine:epsilon-N-L-lysine methyltransferase, has been purified from N. crassa to near homogeneity as judged by column chromatography, polyacrylamide gel electrophoresis, and ultracentrifugation. This protein catalyzes all three methylation reactions. The reaction rates are: A less than B less than C. Sedimentation equilibrium and molecular filtration give a molecular weight of 22,000 for the protein. Sedimentation equilibrium analysis of the protein in 6 M guanidine hydrochloride and sodium dodecyl sulfate-polyacrylamide gel electrophoresis do not detect the possibility of subunit structure. The enzyme contains no half-cystine but does contain several acidic residues. The protein exhibits an absorption band between 400 and 420 nm which is 40 to 50 times less than the absorption seen at 280 nm and is not affected by the presence of substrates. The source of this absorption in unkown.

Amino Acids↗
PubMed1977

Muscle carnitine levels in neuromuscular disease.

The production of energy in muscle from long-chain fatty acid oxidation is dependent upon the presence of carnitine. An abnormally low level of muscle carnitine, as seen in patients with the carnitine deficiency syndrome, results in marked muscle weakness. Muscle from 83 consecutive patients undergoing diagnostic muscle biopsy was assayed for carnitine. Carnitine levels (mean +/- SEM, expressed as nmoles carnitine per mg noncollagen protein) in muscle from patients with Duchenne dystrophy (8.1 +/- 1.7) and possible Becker dystrophy (10.6 +/- 3.0) were significantly (P less than 0.001) different from histologically normal muscle (24.0 +/- 1.4). Carnitine levels in patients with limb-girdle dystrophy (16.1 +/- 3.1) and polymyositis/dermatomyositis (16.6 +/- 3.2) were also low, although not as low as in Duchenne dystrophy. Carnitine levels from patients with denervation atrophy (22.1 +/- 3.6), nonspecific fiber atrophy (21.3 +/- 1.3), and a group of miscellaneous neuromuscular diseases (20.4 +/- 1.4) were not significantly different from histologically normal muscle. The low values of carnitine seen in Duchenne dystrophy and a group of possible Becker dystrophy patients may be a nonspecific effect, related to severe muscle damage.

Carnitine↗
PubMed1976

Regulatory mutants and control of cysteine biosynthetic enzymes in Salmonella typhimurium.

The cysB region in Salmonella typhimurium regulates in a positive manner the noncontiguous structural genes for the enzymes responsible for sulfate reduction in cysteine biosynthesis. We treated three cysB mutants with chemical mutagens and selected 81 secondary mutants in which the inability to utilize sulfate was suppressed. Growth experiments on the suppressed mutants showed that the original loss of sulfate utilization had been corrected to varying degrees and that portions of the pathway had been established in abnormal relationship to one another. Sixty of the suppressed mutations were mapped via transductional analysis, and each was very closely linked to the original cysB mutation. We demonstrated that the cysB product functions in the regulation of the cysteine biosynthetic enzymes during both logarithmic growth and stationary phase. Mutation can alter the regulatory response of one enzyme in either an upward or downward direction while the regulation of other enzymes in the pathway remains unchanged. These data are consistent with the idea of a multivalent or multisite regulator molecule.

Cell-Free System↗