Biomedical subjects

D J Mann

Publications and source records attributed to D J Mann.

6 recordsLinked to original sources

PubMed1992

Mammalian protein serine/threonine phosphatase 2C: cDNA cloning and comparative analysis of amino acid sequences.

Complementary DNA encoding rat protein phosphatase 2C alpha was obtained from a liver library and used to isolate the homologous cDNAs from rabbit liver and human teratocarcinoma libraries. The amino acid sequences of the three enzymes deduced from the cDNA (382 amino acids) were extremely similar (greater than 99% identity), the maximum number of differences (between rat and human) being four. Amino acid sequences of peptides corresponding to 238 residues (61%) of the protein phosphatase 2C beta isoform from rabbit skeletal muscle were determined and showed 12 differences from the recently published sequence of the rat liver enzyme deduced from the cDNA (95% identity).

Amino Acid Sequence↗

PubMed1992

Hormonal induction of malic enzyme in rat hepatocytes cultured on laminin-rich gels.

The levels of malic-enzyme mRNA and activity were determined in primary cultures of adult rat hepatocytes maintained on either rat-tail collagen or a laminin-rich substratum. Cells plated on laminin-rich gels exhibited substantially improved patterns of albumin and malic-enzyme expression when compared with cells maintained on rat-tail collagen. Moreover, hepatocytes plated on the laminin-rich matrix displayed marked malic-enzyme inducibility in response to tri-iodothyronine and dichloroacetate, especially in the presence of insulin. However, Northern blot analysis revealed that the ratio of the amounts of the two major malic-enzyme mRNA species (2.0 and 3.1 kb) was reversed when compared with that found in the liver in vivo, the altered levels of these two species being closer to those found in non-hepatic tissues. These findings indicate that, although the hormonal responsiveness of isolated hepatocytes maintained on laminin-rich gels is markedly improved, and approaches the degree of induction demonstrated in the liver in vivo, the mechanisms of control differ, indicating a loss of liver-specific expression.

Animals↗

PubMed1991

Pre-translational control of hepatic malic enzyme expression during the development of the rat.

The expression of hepatic cytosolic malic enzyme in the developing rat has been studied by molecular-biological techniques. Malic enzyme mRNA was barely detectable throughout the neonatal period, but increased to significant levels immediately before weaning. Northern-blot analysis demonstrated that the two major malic enzyme mRNA species displayed non-co-ordinate control during development, with the 2.0 kb form accumulating to a greater extent than the 3.1 kb form. A novel 1.6 kb mRNA species was found to predominate in foetal samples. Tri-iodothyronine treatment of neonatal rats caused premature induction of all three malic enzyme mRNA species. Dietary studies also showed precocious induction of the mRNA with diets high in carbohydrate, but not with those high in fat.

Aging↗

PubMed1991

Skeletal buffer function and symptomatic magnesium deficiency.

A major factor relating to the oversight of neurological dysfunction and seizures caused by magnesium (Mg++) depletion, involves the buffer functions of the skeletal system orchestrated primarily by the parathyroid. A Mg++ depleted subject may appear relatively asymptomatic until a short period after homeostatic responses go into effect. The results can be devastating if not recognized promptly and treated appropriately. This series of events can best be demonstrated in veterinary medicine but we propose that analogous syndromes occur in clinical medicine. Evidence is presented to support the hypothesis that in subjects with parathyroid hyperactivity and Mg++ deficiency, the stimulus of a rise in serum ionic calcium (Ca++), and the resultant inhibition of parathyroid hormone (PTH) secretion, trigger the transfer of Ca++, Mg++ and other ions from the extracellular space into the exchangeable bone compartment. More importantly, there is a transfer of Mg++ ions from the cerebrospinal fluid into the blood and ultimately into the bone compartment. If the gradient is large and the stimulus adequate, neurological signs and symptoms may be induced. The degree of Ca++ and Mg++ depletion of the peripheral bone and the amount and duration of Ca++ ion increase largely determine the duration and severity of symptoms. The symptom complex is facilitated by sympathetic stimulation. An analogous situation may exist with sodium (Na+).

Animals↗

PubMed1990

Protein serine/threonine phosphatases; an expanding family.

Five protein serine/threonine phosphatases (PP) have been identified by cloning cDNA from mammalian and Drosophila libraries. These novel enzymes, which have not yet been detected by the techniques of protein chemistry and enzymology, are termed PPV, PP2Bw, PPX, PPY and PPZ. The complete amino acid sequences of PPX, PPY and PPZ and an almost complete sequence of PPV are presented. In the catalytic domain PPV and PPX are more similar to PP2A (57-69% identity) than PP1 (45-49% identity), while PPY and PPZ are more similar to PP1 (66-68% identity) than PP2A (44% identity). The cDNA for PP2Bw encodes a novel Ca2+/calmodulin-dependent protein phosphatase only 62% identical to PP2B in the catalytic domain. Approaches for determining the cellular functions of these protein phosphatases are discussed.

Amino Acid Sequence↗

PubMed1986

Modification of WR-2721 toxicity and radioprotection by an inhibitor of alkaline phosphatase.

We used levamisole, an inhibitor of alkaline phosphatase, to study the role of that enzyme in mediating the metabolic activation, toxicity, and radioprotection of WR-2721 in intact mice. We found the toxicity of WR-2721 was slightly decreased by prior subcutaneous (SQ) injection of 40 mg/kg of levamisole. In studying the effect of levamisole on WR-2721 radioprotection, we found that intraperitoneal (i.p.) injection of levamisole had little or no effect on radioprotection of the gastrointestinal and the hematopoietic systems. Even this small reduction of protection was due in part to the toxicity of levamisole as demonstrated when levamisole was injected following, rather than before, WR-2721-radiation treatment. To determine whether levamisole inhibited the activation (i.e., dephosphorylation) of WR-2721 to WR-1065, we assayed WR-1065 in the jejunum using an HPLC electrochemical assay. SQ injection of 75 mg/kg levamisole 10 min prior to WR-2721 reduced the WR-1065 observed 10 min after WR-2721 administration by 37%. In conclusion, levamisole appears to be too toxic and non-specific to be useful in studying and regulating the metabolism, toxicity and radioprotection of WR-2721.

Alkaline Phosphatase↗