A rapid and reliable method for Pb isotopic analysis of peat and lichens by laser ablation-quadrupole-inductively coupled plasma-mass spectrometry for biomonitoring and sample screening.

An analytical protocol for rapid and reliable laser ablation-quadrupole (LA-Q)- and multi-collector (MC-) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of Pb isotope ratios ((207)Pb/(206)Pb and (208)Pb/(206)Pb) in peats and lichens is developed. This technique is applicable to source tracing atmospheric Pb deposition in biomonitoring studies and sample screening. Reference materials and environmental samples were dry ashed and pressed into pellets for introduction by laser ablation. No binder was used to reduce contamination. LA-MC-ICP-MS internal and external precisions were <1.1% and <0.3%, respectively, on both (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios. LA-Q-ICP-MS internal precisions on (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were lower with values for the different sample sets <14.3% while external precisions were <2.9%. The level of external precision acquired in this study is high enough to distinguish between most modern Pb sources. LA-MC-ICP-MS measurements differed from thermal ionisation mass spectrometry (TIMS) values by 1% or less while the accuracy obtained using LA-Q-ICP-MS compared to solution MC-ICP-MS was 3.1% or better using a run bracketing (RB) mass bias correction method. Sample heterogeneity and detector switching when measuring (208)Pb by Q-ICP-MS are identified as sources of reduced analytical performance.

Biogeochemical signatures in the lichen Hypogymnia physodes in the mid Urals.

Multi-element content and uranium (U) isotopes were investigated in the lichen Hypogymnia physodes (native and transplants) sampled across a 60-km transect, centred on Karabash smelter town, from Turgoyak Lake (SW) to Kyshtym (NE) to investigate the origin of U. Kyshtym was the site of a major nuclear accident in 1957. (234)U/(238)U activity ratios in native thalli sampled during July 2001 were within the natural isotopic ratio in minerals. Uranium/thorium (U/Th) ratios were higher in native thalli towards the NE (average 0.73) than those in the SW (average 0.57). Element signatures in native thalli and transplants suggest U was derived from fossil fuel combustion from Karabash and sources lying further to the east. Systematic and significant U enrichment indicative of a nuclear fuel cycle source was not detected in any sample. Element signatures in epiphytic lichen transplants and native thalli provide a powerful method to evaluate U deposition.

A new astrophysical setting for chondrule formation.

Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.

Preparation of Bruch's membrane and analysis of the age-related changes in the structural collagens.

AIMS/BACKGROUND: The morphological changes in Bruch's membrane and its constituent collagen seen during aging have been studied extensively but the chemical nature of the collagen and any aging changes have not previously been evaluated. METHODS: A method for preparing purified Bruch's membrane from human cadaver eyes by dissection preceded by trypsin digestion was developed. Following pepsin digestion, the constituent collagens were analysed by SDS-PAGE and by immunoblotting. Cyanogen bromide digestion was used to ascertain the solubility of the collagen and the proportion of type I to type III collagen. After hydrolysis of Bruch's membrane samples the constituent amino acids and collagen crosslinks were measured. RESULTS: The presence of collagen types I, III, IV, and V in Bruch's membrane was confirmed. The proportion of type III collagen as a percentage of total fibrous collagens was calculated as being between 35% and 39%, with no significant difference between different macular and peripheral sites or with age. There was a highly significant decline in the solubility of Bruch's membrane collagen with age, from near 100% in the first decade of life to 40-50% in the ninth decade at both macular and peripheral sites. There was no significant change in the amount of enzymatically formed collagen crosslinks with age. Amino acid analysis indicated a significant increase in the amount of non-collagen protein with age in macular but not peripheral sites. CONCLUSION: Changes in the constituent collagens may contribute to the accumulation of debris in Bruch's membrane with age and interfere with the function of the retinal pigment epithelium, with subsequent consequences for the overlying photoreceptors.

The effect of nucleotide upon a specific isomerization of actomyosin subfragment 1.

The binding of actin to myosin subfragment 1 (S1) has been shown to occur as a two-step reaction [Coates, Criddle & Geeves (1985) Biochem. J. 232, 351-356]. In the first step actin is weakly bound and the second step involves the complex isomerizing to a more tightly bound state. This isomerization can be followed specifically by monitoring the fluorescence of actin that has been covalently labelled with N-(pyren-1-yl)-iodoacetamide at Cys-374 [Geeves, Jeffries & Millar (1986) Biochemistry 25, 8454-8458]. We report here that the presence of nucleotides and nucleotide analogues affects the equilibrium between the strongly bound and weakly bound states (referred to as K2). In the presence of ATP, [gamma-thio]ATP or ADP and vanadate a value of approx. less than 10(-2) was estimated for K2. In the presence of PPi or ADP a value of approx. 2.3 or 10 respectively was obtained. An increase in KCl concentration or the presence of 40% ethylene glycol was found to decrease K2 in the presence of ADP. The data presented here are consistent with the two-step binding model proposed by Geeves, Goody & Gutfreund [(1984) J. Muscle Res. Cell Motil. 5, 351-361], where it was suggested that the transition between weakly bound and strongly bound states is closely associated with the force-generating event in whole muscle.

ATP-induced dissociation of rabbit skeletal actomyosin subfragment 1. Characterization of an isomerization of the ternary acto-S1-ATP complex.

The adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) induced dissociation of actomyosin subfragment 1 (S1) has been investigated by monitoring the light scattering changes that occur on dissociation. We have shown that ATP gamma S dissociates acto-S1 by a mechanism similar to that of ATP but at a rate 10 times slower. The maximum rate of dissociation is limited by an isomerization of the ternary actin-S1-nucleotide complex, which has a rate of 500 s-1 for ATP gamma S and an estimated rate of 5000 s-1 for ATP (20 degrees C, 0.1 M KCl, pH 7.0). The activation energy for the isomerization is the same for ATP and ATP gamma S, and both show a break in the Arrhenius plot at 5 degrees C. The reaction between acto-S1 and ATP was also followed by the fluorescence of a pyrene group covalently attached to Cys-374. We show that the fluorescence of the pyrene group reports the isomerization step and not actin dissociation. The characterization of this isomerization is discussed in relation to force-generating models of the actomyosin cross-bridge cycle.