The neutrophil enzyme myeloperoxidase uses H2O2 to oxidize chloride, bromide, iodide and thiocyanate to their respective hypohalous acids. Chloride is considered to be the physiological substrate. However, a detailed kinetic study of its substrate preference has not been undertaken. Our aim was to establish whether myeloperoxidase oxidizes thiocyanate in the presence of chloride at physiological concentrations of these substrates. We determined this by measuring the rate of H2O2 loss in reactions catalysed by the enzyme at various concentrations of each substrate. The relative specificity constants for chloride, bromide and thiocyanate were 1:60:730 respectively, indicating that thiocyanate is by far the most favoured substrate for myeloperoxidase. In the presence of 100 mM chloride, myeloperoxidase catalysed the production of hypothiocyanite at concentrations of thiocyanate as low as 25 μM. With 100 μM thiocyanate, about 50% of the H2O2 present was converted into hypothiocyanite, and the rate of hypohalous acid production equalled the sum of the individual rates obtained when each of these anions was present alone. The rate of H2O2 loss catalysed by myeloperoxidase in the presence of 100 mM chloride doubled when 100 μM thiocyanate was added, and was maximal with 1 mM thiocyanate. This indicates that at plasma concentrations of thiocyanate and chloride, myeloperoxidase is far from saturated. We conclude that thiocyanate is a major physiological substrate of myeloperoxidase, regardless of where the enzyme acts. As a consequence, more consideration should be given to the oxidation products of thiocyanate and to the role they play in host defence and inflammation.

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In the presence of pyrithione, which was used as a Zn *+ ionophore, Znzf (l&l00 PM) increased phorbol ester binding by intact B-CLL cells in a dose-dependent fashion. Zn pyrithione increased 2-fold the number of phorbol ester receptors in B-cells (0.74 to 1.4 pmol/lV cells), neutrophil polymorphs (0.2 to 0.51 pmol/lW cells) and platelets (91 to 209 pmol/lOiO cells). Fractionation of cells after treatment with Zn pyrithione showed that increased binding of PDBu occurred in the particulate fraction of cells and this was accompanied by loss of phorbol ester receptors from the cytosol. These data are compatible with a role for Zn in the subcellular distribution and activation of protein kinase C.

A series of complexes of the general formulae RaPAu(6-mp), R3P = Et3P, Ph3P, Cy3P, PhMezP, (0-tol)3P, (m-tol)3P or (p-tol)3P, (AuC1)Ph2P(CH2),PPh2(Au(6-mp)), n = 2 or 3, and P~~P(CH~),PP~Z(AU(~-~~))~, n = 1, 2 or 3 and 6-mp is the anion derived from 6-mercaptopurine (purine-6-thiol), have been prepared and characterized by spectroscopic methods (i.r., 'H, 13c, 31P n.m.r. and f.a.b. m.s.) and, in the case of the PhsPAu(6-mp) complex, by single-crystal X-ray diffraction methods. The spectroscopic data show that the 6-mp ligand coordinates as a thiolate ligand and that the gold atoms exist in linear P-Au-S (or P-Au-C1) geometries. This has been confirmed by an X-ray study on Ph3PAu(6-mp), isolated as an ethanol solvate; the study shows the gold atom to be linearly coordinated by the phosphorus and sulfur atoms: Au-P(1) 2.237 (2), Au-S(6) 2.287(1) A and P-Au-S 173.71(6)'. Crystals of PhsPAu(6-mp).EtOH are triclinic, space group P i , with unit cell dimensions a 11.066(3), b 13.552(3), c 8.705(2) A, a: 91.51(2), , O 113.06(2), y 89.69(2)', V 1200.8(5) A3, Z 2. The structure was refined by a full-matrix least-squares procedure to R 0.034 for 3978 reflections with I > 3 . 0 4 I ) . Preliminary results of testing for antiarthritic activity among the new complexes in rats are also reported showing that some of them are more potent/less toxic than current gold(1) thiolates used clinically. Ph2P(CH2)2PPh2(Au(6-mp))z.2Hz0 off-white PhzP(CH~)3PPhz(Au(6-mp))z.CHzClz off-white --A With decomposition.

A combination of 65Zn-tracer determinations, oxidative analyses for glycerol, and a bioassay for uncomplexed Zn2+ have shown that: (i) zinc monoglycerolate (ZMG) dissolves in aqueous salt solutions/physiological media by dissociation into zinc ions and glycerol, but the rate and extent of ZMG dissolution depend upon pH, and/or concentration and complexing efficiency of zinc-ligands; (ii) under physiological conditions certain ligands present in skin and blood (e.g. citrate, lactate, albumin, histidine, glutathione and other thiols and, to a lesser extent, amino acids) accelerate ZMG dissolution; and (iii) there is a general correlation between the conditional stability constants (pH 7.3, 25 degrees C) of zinc-ligand complexes and the ability of given ligands to (a) solubilize ZMG in vitro and (b) mask the irritancy of Zn2+ in vivo. These observations indicate a mechanism for the transformation of ZMG applied transdermally or subcutaneously, to bioactive zinc (anti-arthritic nutritional supplement, etc.).