Effect of epinephrine on the oxidative desaturation of fatty acids in the rat.

The effect of epinephrine on the oxidative desaturation of fatty acids by liver microsomal preparations of rats has been studied. Administration of epinephrine (1 mg/kg body weight) produced a significant decrease in desaturation of [l-14C]=linoleic acid to gamma-linolenic acid and of [L-14C]alpha-linolenic acid to actadeca-6,9,12,15-tetraenoic acid 12 hr after the infection. Lower doses produced a lesser effect on the delta6-desaturation activity. Epinephrine administration modified the V max of linoleic acid desaturation but not the K m. There was also a slight increase in palmityl desaturation activity. The effect of epinephrine on delta6-desaturation activity was postulated to be mediated through an enhancement of the intracellular cyclic AMP levels that lead to an increase of a glucose metabolite. This metabolite would inhibit delta6-desaturation activity.     

Hypoxanthine-guanine phosphoribosyl transferase deficiency

Summary In man congenital lack of an enzyme of the purine salvage system, hypoxanthineguanine phosphoribosyl transferase (HG-PRT E.C. 2.4.2.8), is mostly accompanied by a picture known as the Lesch-Nyhan syndrome. The degree of deficiency may vary from zero to a few percent of normal activity but a correlation between the severity of HG-PRT deficiency and the clinical picture has not been observed, no more than a correlation between HG-PRT deficiency and neurological dysfunction. But individuals with undetectable HG-PRT activity but without the Lesch-Nyhan syndrome have been described. Patients with partial HG-PRT deficiency have clinically distinctive findings. Sometimes mild neurological abnormalities are observed. Because of marked overproduction of uric acid severe gouty arthritis and renal dysfunction are often encountered in both complete and partial deficiency.There is considerable molecular heterogeneity in HG-PRT deficiency in man. Mutant enzymes may exhibit different kinetic and electrophoretic properties, indicating that there might be a mutation on the structural gene coding for HG-PRT.Lack of HG-PRT disturbs purine interconversions profoundly. In addition to an important function of HG-PRT in the uptake of the purine bases hypoxanthine and guanine into the cell, the effective uptake of inosine, guanosine and adenosine also seems to be dependent on HG-PRT. Uptake of purine bases into intact red blood cells occurs according to a two component mechanism, one component probably involving a phosphoribosyl transferase system.The inheritance of HG-PRT deficiency is X-linked recessive and it is transmitted by asymptomatic carrier females. Several methods have been introduced for carrier detection. As a consequence of X chromosome inactivation, in these females a mosaicism of HG-PRT positive and HG-PRT negative fibroblasts can be demonstrated after cloning or after selection of HG-PRT negative cells in a selective medium. A more rapid method involves direct measurements of HG-PRT activities in single hair roots from the scalp. Because hair roots develop more or less clonally, in heterozygote females HG-PRT positive and negative hair roots are encountered. HG-PRT deficiency can be detected antenatally by demonstrating the presence or absence of enzyme activity in ammiotic fluid derived fibroblasts qualitatively by autoradiography and quantitatively by ultramicrochemical measurements of enzyme activities in single or small numbers of cells.In studies with isolated cells the metabolic defect can be corrected in several ways. Metabolic cooperation between HG-PRT positive and HG-PRT negative cells leads to apparently normal phenotype of all cells, provided there is cell to cell contact. There is evidence that a missing enzyme product or a derivative might be transferred from the normal to the mutant cells. Apparent correction of the enzyme defect is also observed when HG-PRT deficient lymphocytes are stimulated with phytohaemagglutinin.The first data suggestive of genetic complementation between two human HG-PRT deficient cell strains by which hybrid cells can synthesize a functionally active HG-PRT, are consistent with the view that HG-PRT deficiency in man is due to a structural gene mutation. Recent results show that other interesting findings might come from experiments in which HG-PRT deficient cells are treated with exogenous genetic material (isolated DNA or metaphase chromosomes) to reactivate or induce HG-PRT activity.Supported by grants from FUNGO (Foundation for Medical Scientific Research in the Netherlands) and the Medical Prevention Fund.     

A bead and spring model for the stiffness of DNA.

The chain stiffness of linear native DNA is represented by a generalized bead and spring model recently proposed. It incorporates molecular rigidity by means of springs between beads, which are second neighbors along the contour of the chain. These springs are equivalent to elastic forces having longitudinal and transversal contributions. The model is compared with existing experimental data of sedimentation and low-angle light scattering to obtain the statistical parameters of DNA. The value of the statistical length obtained with this model is 1300 Å. The same value is obtained with the wormlike chain. Throughout this analysis, excluded volume is left out as a simplifying assumption.     

Catecholamine-ouabain interaction on the isolated perfused rat heart.

The effect of catecholamine-depleting pretreatments, reserpine, and 6-hydroxydopamine (6-OH-DA) on left ventricular pressure (LVP) and the inotropic response to graded doses of ouabain (up to 300 mug/0.05 ml) was studied in isolated perfused rat and guinea-pig hearts. In rats, reserpine and 6-OH-DA depleted the cardiac content of catecholamine, but did not increase initial LVP and did not reduce the inotropic response to the highest dose of ouabain. It is concluded that in isolated rat hearts, these catecholamine-depleting pretreatments nearly abolish the inotropic response to ouabain, and this effect appears to be mediated mainly through an increase in initial LVP. The reason why catecholamine depletion failed to increase initial LVP in guinea pigs remains unexplained.     

Molecular basis of chromosome banding

Silver and mercury ions are known to react with the bases of nucleic acids in solution. At low cation/base ratios Ag+ has an affinity for GC pairs in DNA, whereas Hg++ is preferentially bound to AT-rich nucleic acids. We have used fluorometry to measure the effect of these cations on the fluorescence intensity of preformed complexes of acranil and DNA in solution. The results are: 1) Ag+ enhances the fluorescence intensity presumably by affecting the dye intercalated in the vicinity of GC-pairs. 2) The addition of Hg++ leads to a quenching of the fluorescence intensity of the complex at low ion/base ratios, suggesting an effect on the dye molecules bound to AT pairs. At high GC-content of the nucleic acid, slight enhancement of the fluorescence intensity occurs with Hg++. 3) With both metals there is a correlation between base content of DNA and effect on the intensity of fluorescence indicating base specificity of the dye-polymer interaction.     

A new variant of glucosephosphate isomerase deficiency.

A new variant of glucose-6-phosphate isomerase deficiency is described. The enzyme kinetics and properties were studied. Genetic and electrophoretic data pointed to a double heterozygous state in the patient. These data are compared to the other variants described in the literature until now.