Jonathan S. Dixon

Interactions of blood metalloproteins with nitrogen oxides and oxidant air pollutants

Abstract The effects of in vitro exposure of fresh blood and in vivo exposure of animals to atmospheres containing NO, NO2, or O3 were examined on the iron- and copper-containing proteins in whole blood by low-temperature EPR spectroscopy. Exposure of whole blood to NO under conditions in which neither free nor bound O2 is present results in the quantitative conversion of Hb to the Hb-NO derivative. Subsequent exposure of the derivative to air converts nearly all of the Hb-NO to methemoglobin in the reaction whose mechanism is detailed in this report. Nitrite seems to participate only in the terminal stages. In vivo exposure of animals to air containing a few parts per million NO or NO2 gives rise to significant accumulations of both Hb-NO and methemoglobin, the latter being the major product. This effect can be seen under typical ambient conditions. Exposure to NO2, either aerobically or anaerobically, gives rise to a mixture of Hb-NO and methemoglobin in the ratio which ranges between 1:4 and 1:20. Methemoglobin is invariably the major product. Exposure to O3, on the other hand, fails detectably to alter the state of hemoglobin in whole blood, nor does O3 generate a measurable change in organic free radicals. All three gases — NO, NO2, and O3 — significantly increase the signal due to high-spin ( S = 5 2 ) ferric catalase, while NO, NO2, and O3 all depress the level of iron transferrin. These effects translate into decreased activity for both proteins. Other metalloproteins in blood which are observable by EPR spectroscopy are, for the most part, insensitive to NO, NO2, or O3. The implications of these chemical changes in terms of health effects of NOx and oxidant air pollution are discussed.

Retention of the Biological Potency of Human Pituitary Growth Hormone After Reduction and Carbamidomethylation

The reduced alkylated derivative of human pituitary growth hormone was prepared by reacting the native hormone in 8M urea solution, first with mercaptoethanol and then with iodoacetamide. On the basis of amino acid analyses, the product isolated after gel filtration on Sephadex G-100 is completely devoid of unreduced cystine but otherwise has a composition identical to that of the native hormone. When assayed in both the rat tibia test and the pigeon crop-sac assay,it appears that the full potency of the native hormone is retained in the reduced alkylated derivative.

The isolation and structure of β-melanocyte-stimulating hormone from horse pituitary glands

Abstract The complete amino acid sequence in equine β-melanocyte-stimulating hormone has been determined on highly purified material isolated from the neurointermediate lobes of horse pituitaries. In the final purification step (countercurrent distribution in 0.1% acid- n -butanol-pyridine, 11:5:3 v v ), as well as in zone electrophoresis at pH 4.9 on starch, this material behaved like bovine β-melanocyte-stimulating hormone; however, complete amino acid analysis of the hormone, as well as the elucidation of the structure of the peptide fragments isolated from chymotryptic and tryptic digests of the equine β-melanocyte-stimulating hormone, revealed its unique structure to be H-Asp.Glu.Gly.Pro.Tyr.Lys.Met.Glu.His.Phe.Arg.Try.Gly. Ser.Pro.Arg.Lys.Asp-OH. Although the sequence differs somewhat from that found in any other naturally occurring melanocyte-stimulating pituitary hormone (see Fig. 3), it still contains the nonvarying internal heptapeptide sequence… Met.Glu.His.Phe.Arg.Try.Gly… found in each of these hormones. On the basis of results of bioassay, it was concluded that the nature of the NH 2 -terminal sequence in β-melanotropins is far more important for the in vivo melanocyte stimulation than is the amino acid composition near the COOH terminus.

Chemistry of prolactin

Summary The present status of the chemistry of prolactin obtained from ovine pituitary glands has been reviewed. The phenomenon of polymerization of the molecule has been emphasized. Recent experiments resulting in the isolation of monomeric prolactin were described.