Benzene and the risk of non-Hodgkin lymphoma: A review and meta-analysis of the literature

Benzene, an accepted leukemogen, has been suggested to cause other hemato- and lymphopoietic cancers. Here we review the published literature for non-Hodgkin lymphoma (NHL) and occupational exposure to benzene. Six cohorts, sixteen case–control studies and two studies of other designs were identified through keyword searches of bibliographic databases. Twenty-two of twenty-four studies found no association between NHL and ever exposed to benzene compared to never; a random-effects meta-analysis gave a pooled risk estimate of 1.11 (95% confidence interval 0.94–1.30). Our finding of no effect agrees with one of two previous meta-analyses. The other meta-analysis examined if high benzene exposure increased NHL risk but a lack of consistent exposure categories within the same metric should have precluded pooling risks by exposure level. Instead, we reviewed whether dose–response relationships existed. The best available data came from six studies where exposure was estimated from historical measurements and on the whole, no trends in risks of NHL with rising cumulative, average, peak, or duration of benzene exposure were found. NHL is a heterogeneous group of malignancies and although less well-studied, benzene was not associated with any NHL subtype. In conclusion, benzene at either low or high doses does not increase the risk of NHL.     

Intrinsic fluorescence of elongation factor Tu in its complexes with GDP and elongation factor Ts

The intrinsic fluorescence properties of elongation factor Tu (EF-Tu) in its complexes with GDP and elongation factor Ts (EF-Ts) have been investigated. The emission spectra for both complexes are dominated by the tyrosine contribution upon excitation at 280 nm whereas excitation at 300 nm leads to exclusive emission from the single tryptophan residue (Trp-184) of EF-Tu. The fluorescence lifetime of this tryptophan residue in both complexes was investigated by using a multifrequency phase fluorometer which achieves a broad range of modulation frequencies utilizing the harmonic content of a mode-locked laser. These results indicated a heterogeneous emission with major components near 4.8 ns for both complexes. Quenching experiments on both complexes indicated limited accessibility of the tryptophan residue to acrylamide and virtually no accessibility to iodide ion. The quenching patterns exhibited by EF-Tu-GDP and EF-Tu X EF-Ts were, however, different; both quenchers were more efficient at quenching the emission from the EF-Tu x EF-Ts complex. Steady-state and dynamic polarization measurements revealed limited local mobility for the tryptophan in the EF-Tu x GDP complex whereas formation of the EF-Tu x EF-Ts complex led to a dramatic increase in this local mobility.     

Aroid scarabs in the genus Peltonotus Burmeister (Coleoptera,Scarabaeidae, Dynastinae): key to species and new distributional data

The southeast Asian scarab beetle genus Peltonotus Burmeister (Scarabaeidae, Dynastinae, Cyclocephalini) is reviewed. New country records for Peltonotus morio Burmeister (Myanmar and Vietnam), Peltonotus nasutus Arrow (southern China and Cambodia), and Peltonotus favonius Jameson and Wada (Myanmar) are reported, including a new record in the Palearctic/Sino-Japanese biogeographic region. The first female specimen of Peltonotus favonius is described. Biological associations with aroid inflorescences are reviewed, and human consumption of Peltonotus beetles is reported. A key to all species, paralectotype designations for Peltonotus nasutus, diagnoses, and distributions using dynamic mapping tools are included.     

Interaction of a fluorescent analogue of GDP with elongation factor Tu: steady-state and time-resolved fluorescence studies

A fluorescent derivative of GDP was prepared by the reaction of 2'-amino-2'-deoxy-GDP with fluorescamine. This derivative binds tightly (KD approximately 4.5 X 10(-8) M) to elongation factor Tu (EF-Tu) from Escherichia coli. The emission properties, including spectra, polarizations, and lifetimes, for fluorescamine-GDP free in solution and bound to EF-Tu are presented. Emission data on the fluorescamine-ethylamine conjugate are also given. A multifrequency phase and modulation lifetime study (using nine modulation frequencies over the range of 2-80 MHz) indicated that the emissions of these three systems were well characterized by single exponential decays corresponding to 1.45 ns for the fluorescamine-ethylamine derivative in buffer and to 7.74 and 11.03 ns for the fluorescamine-GDP derivative free in buffer and bound to EF-Tu, respectively. Multifrequency differential polarized phase fluorometry results indicated a rotational relaxation time of the protein-probe complex of approximately 88 ns; these data also indicated the lack of significant local motion for the probe. Addition of excess GDP to the EF-Tu-probe complex led to displacement of the fluorescamine-GDP derivative as evidenced by the change in both the steady-state and dynamic polarization values. The observed increase in fluorescence intensity upon displacement allowed us to follow the kinetics of the dissociation reaction; a dissociation rate constant of 5.0 X 10(-3) S-1 was determined. These results demonstrate the utility of this 2'-amino-2'-deoxy-GDP analogue as a probe of guanosine nucleotide dependent systems.     

Time-resolved fluorescence studies on the ternary complex formed between bacterial elongation factor Tu, guanosine 5'-triphosphate, and phenylalanyl-tRNAPhe

Time-resolved fluorescence spectroscopy was used to investigate the solution dynamics of Escherichia coli tRNAPhe, Phe-tRNAPhe, and Phe-tRNAPhe associated with GTP and elongation factor Tu (EF-Tu) in a ternary complex. Two fluorescence probes were employed: fluorescein, covalently bound to Phe-tRNAPhe at the s4U8 base (Phe-tRNAPhe-Fl8), and ethidium bromide, noncovalently associated with the tRNA (EB.Phe-tRNAPhe). The lifetimes observed for ethidium bromide were 1.89 ns, free in solution, and 26.3 ns, bound to its tight binding site on tRNA. Fluorescein-labeled tRNA had a lifetime of 4.3 ns, with no significant difference among the values for aminoacylated, unacylated, and EF-Tu-bound Phe-tRNAPhe-Fl8. Differential phase and modulation data for each fluorophore-tRNA system were fit with local and global Debye rotational relaxation times. Local motion of the labeled fluorescein in Phe-tRNAPhe-Fl8, tRNAPhe-Fl8, and Phe-tRNAPhe-Fl8.EF-Tu.GTP was characterized by rotational relaxation times of 2.7 +/- 0.5, 2.4 +/- 0.4, and 2.4 +/- 0.1 ns, respectively. These values are equal, within experimental error, and suggest that the rotational mobility of the s4U8-conjugated dye is unaffected by either tRNAPhe aminoacylation or ternary complex formation. Global rotational relaxation times for Phe-tRNAPhe-Fl8, 97 ns, and EB.Phe-tRNAPhe, 140 ns, were equivalent to those determined for the unacylated species, denoting little change in the overall size or shape of the tRNA molecule upon aminoacylation. These values for (Phe-)tRNA were larger than expected for a hydrated sphere of equivalent volume, 83 ns, and therefore confirm the asymmetric nature of the tRNA structure in solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Divergent responses of gonadotropin subunit messenger RNAs to continuous versus pulsatile gonadotropin-releasing hormone in vitro

Episodic GnRH input is necessary for the maintenance of LH and FSH secretion. In the current study we have assessed the requirement of a pulsatile GnRH signal for the regulation of gonadotropin alpha- and beta-subunit gene expression. Using a dispersed rat pituitary perifusion system, GnRH (10 nM) was administered as a continuous infusion vs. hourly pulses. Secretion of free alpha-subunit, LH, and FSH were monitored over 5-min intervals for the entire 12-h treatment period before the responses of alpha, LH beta, and FSH beta mRNAs were assessed. Basal release of all three glycoproteins declined slowly over 6-8 h before reaching a plateau. The cells were responsive to each pulse of GnRH, but continuous GnRH elicited only a brief episode of free alpha-subunit, LH, and FSH release, followed by a return to unstimulated levels. Despite the similar patterns of secretion, differences were observed in the responses of gonadotropin mRNAs to the two modes of GnRH. alpha mRNA increased in response to continuous (1.6-fold) or pulsatile (1.7-fold) GnRH. FSH beta mRNA was suppressed to 48% of the control value after continuous GnRH, but was stimulated over 4-fold by the pulses. LH beta mRNA was unresponsive to either treatment paradigm. We conclude that in vitro 1) alpha mRNA levels are increased in response to GnRH independent of the mode of stimulation; 2) under the conditions studied, LH beta mRNA levels are unresponsive to either mode of GnRH input; and 3) the response of FSH beta mRNA to GnRH is highly dependent on the mode of administration, with levels depressed in response to continuous GnRH, but stimulated by pulsatile GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)