The periplasmic Fe-hydrogenase from Desulfovibrio vulguris (Hildenborough) contains three ironsulfur prosthetic groups : two putative electron transferring [4Fe-4S] ferredoxin-like cubanes (two Fclusters), and one putative Fe/S supercluster redox catalyst (one H-cluster). Combined elemental analysis by proton-induced X-ray emission, inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, atomic absorption spectroscopy and colorimetry establishes that elements with Z > 21 (except for 12-15 Fe) are present in 0.001-0.1 mol/mol quantities, not correlating with activity. Isoelectric focussing revmIs the existence of multiple charge conformers with PI in the range 5 7-6.4. Repeated re-chromatography results in small amounts of enzyme of very high H,-production activity determined under standardized conditions (z 7000 Ujmg). The enzyme exists in two different catalytic forms: as isdated the protein is 'resting' and 02-insensitive; upon reduction the protein becomes active and 02-sensitive. EPR-monitored redox titrations have been carried out of both the resting and the activated enzyme. In the course of a reductive titration, the resting protein becomes activated and begins to produce molecular hydrogen at the expense of reduced titrant. Therefore, equiiibrium potentials are undefined, and previously reported apparent The iron-sulfur protein hydrogenase catalyzes the reversible activation of molecular hydrogen, a process involving the transfer of two electrons. Most presently known hydrogenases are also nickel proteins. The nickel ion is generally assumed to be the redox-active catalytic center [l, 21. A small subclass is formed by the Fe-hydrogenases; these enzymes presumably contain no other potentially redox active transition metals than iron [3]. By exclusion, this implies that the H2 activation is located on an iron-sulfur cluster. Redox catalysis is not Correspondence to W.

Platinum distribution was studied in rat peritoneal tumors after i.p. treatment with equimolar doses of carboplatin and cisplatin. Low platinum concentrations (4 ppm) were detected in the periphery of the tumor after carboplatin treatment, whereas no platinum was detected 0.5 mm in from the periphery. In contrast, after cisplatin treatment, high platinum concentrations (29 ppm) were measured in the periphery of the tumor and moderate concentrations (14 ppm) were measured in the center. Only following increased carboplatin doses were low platinum concentrations detectable in the tumor. The total platinum concentration in the tumors was determined after equimolar administration of both drugs. In all, 7 times more platinum was detected after cisplatin treatment than after carboplatin treatment, and 10 times more carboplatin than cisplatin had to be injected to obtain comparable platinum concentrations in the tumors. When single cells were incubated with equimolar concentrations of carboplatin and cisplatin, 6-7 times more platinum was found in cells treated with cisplatin. However, pharmacokinetic studies favored i.p. administration of carboplatin because the clearance of this compound from the peritoneal cavity, expressed as t1/2 beta, was lower than that of cisplatin (239 vs 78 min), resulting in an AUC in the peritoneal cavity for both total and ultrafiltered drug that was almost 3 times higher for carboplatin than cisplatin. The AUC for ultrafiltered carboplatin in plasma was 2-fold that for cisplatin (2,801 +/- 210 vs 1,334 +/- 431 microM m). The present study demonstrated that in spite of the pharmacological advantages of carboplatin, its capacity to penetrate into peritoneal tumors and tumor cells is far lower than that of cisplatin.

Although calcium (Ca) precipitation may play a pathogenic role in atherosclerosis, information on temporal patterns of microcalcifications in human coronary arteries, their relation to expression of calcification-regulating proteins, and colocalization with iron (Fe) and zinc (Zn) is scarce. Human coronary arteries were analyzed post mortem with a proton microprobe for element concentrations and stained (immuno)histochemically for morphological and calcification-regulating proteins. Microcalcifications were occasionally observed in preatheroma type I atherosclerotic intimal lesions. Their abundance increased in type II, III, and IV lesions. Moreover, their appearance preceded increased expression of calcification-regulating proteins, such as osteocalcin and bone morphogenetic protein-2. In contrast, their presence coincided with increased expression of uncarboxylated matrix Gla protein (MGP), whereas the content of carboxylated MGP was increased in type III and IV lesions, indicating delayed posttranslational conversion of biologically inactive into active MGP. Ca/phosphorus ratios of the microcalcifications varied from 1.6 to 3.0, including amorphous Ca phosphates. Approximately 75% of microcalcifications colocalized with the accumulation of Fe and Zn. We conclude that Ca microprecipitation occurs in the early stages of atherosclerosis, inferring a pathogenic role in the sequel of events, resulting in overt atherosclerotic lesions. Microcalcifications may be caused by local events triggering the precipitation of Ca rather than by increased expression of calcification-regulating proteins. The high degree of colocalization with Fe and Zn suggests a mutual relationship between these trace elements and early deposition of Ca salts.