The osmotic concentration of parietal muscle of the hagfish Myxine glutinosa L., including estimates of free and bound constituents

The principal osmotic constituents of plasma and of muscle before and after ultracentrifugation have been determined. By analysing the muscle fluid and centrifuged muscle and determining their extracellular fluid (inulin space), ion-binding in the cells was estimated at Na 26%, K 0.3%, Ca 93%, Mg 24%, Cl 21% and P 10%. Muscle fluid was 4.9% (2.7-7.4%) hyperosmotic to plasma. This is discussed in relation to calculated osmolality of muscle and plasma.     

Reductive inactivation of digitoxin by Eubacterium lentum cultures

The obligate anaerobe Eubacterium lentum inactivated the cardiac glycoside digitoxin by reducing the double bond in the lactone ring. This conversion was quantitative when the substrate was incubated at a concentration of 10 micrograms/ml. The reduction reaction coincided with the growth phase of the bacterium. The stereochemical configuration at C-20 of the reduction product dihydrodigitoxin was found to be R. Incubation of digitoxigenin and its mono- and bisdigitoxosides individually with E. lentum led to the formation of their respective dihydro derivatives. The configuration at C-20 of these reduced metabolites was also found to be R.     

Influence of dose and route of administration of bovine follicular fluid and the suppressive effect of purified bovine inhibin (Mr 31,000) on plasma FSH concentrations in ovariectomized ewes

Ovariectomized Merino ewes were used to develop an in-vivo bioassay for purified bovine inhibin of Mr 31,000. Various doses (0.25, 0.5, 1 or 2 ml) of bovine follicular fluid, given either by the intravenous (i.v.) or intracarotid route (i.c.) resulted in significant linear dose-related suppression of plasma FSH and interval to maximum suppression. Control ewes (1.0 ml steer plasma) showed no significant change in FSH over the same period. Doses of 470 and 2590 U of pure inhibin given i.v. caused a significant suppression of FSH in plasma in all ewes. The in-vivo potency estimate of the high dose (2760 U, 1420-4690 fiducial limits) agreed well with the in-vitro assay of potency. There were no significant changes observed in mean plasma LH after treatment with the higher dose of pure inhibin. There were no rebound effects of treatment with bovine follicular fluid or pure inhibin on FSH concentrations above that of controls. It is concluded that the form of bovine inhibin of Mr 31,000, which is believed to be the predominant circulating form, is biologically active when administered in vivo.     

Mentally abnormal offenders: manner of death.

A 23 year follow up of deaths in a population of mentally disordered patients was carried out, and a typical case history is reported. A quarter (71) of the deaths reported were unnatural, verdicts of suicide or accidental death or open verdicts having been recorded. For men in most age groups the proportion of deaths by suicide was two to three times greater than in the general population in 1982; the rate among those aged 25-29 was five times that in the general population. Differences in the rate of unnatural death among diagnostic categories of mental illness were not significant, but the proportion of unnatural deaths among the mentally handicapped will probably eventually be lower than that among psychotic offenders or those with personality disorders. Violent death occurs at an older age in those with affective disorders. Social isolation and alienation add to the handicap of mental disorder in this group of people, and these sometimes difficult but always vulnerable patients must continue to be offered asylum other than prison.     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Interacting proteins identified by genetic interactions: a missense mutation in alpha-tubulin fails to complement alleles of the testis-specific beta-tubulin gene of Drosophila melanogaster.

In this paper we demonstrate that failure to complement between mutations at separate loci can be used to identify genes that encode interacting structural proteins. A mutation (nc33) identified because it failed to complement mutant alleles of the gene encoding the testis-specific beta 2-tubulin of Drosophila melanogaster (B2t) did not map to the B2t locus. We show that this second-site noncomplementing mutation is a missense mutation in alpha-tubulin that results in substitution of methionine in place of valine at amino acid 177. Because alpha- and beta-tubulin form a heterodimer, our results suggest that the genetic interaction, failure to complement, is based on the structural interaction between the protein products of the two genes. Although the nc33 mutation failed to complement a null allele of B2t (B2tn), a deletion of the alpha-tubulin gene to which nc33 mapped complemented B2tn. Thus, the failure to complement appears to require the presence of the altered alpha-tubulin encoded by the nc33 allele, which may act as a structural poison when incorporated into either the tubulin heterodimer or microtubules.     

Binding of the 3'' terminus of tRNA to 23S rRNA in the ribosomal exit site actively promotes translocation.

A key event in ribosomal protein synthesis is the translocation of deacylated tRNA, peptidyl tRNA and mRNA, which is catalyzed by elongation factor G (EF-G) and requires GTP. To address the molecular mechanism of the reaction we have studied the functional role of a tRNA exit site (E site) for tRNA release during translocation. We show that modifications of the 3' end of tRNAPhe, which considerably decrease the affinity of E-site binding, lower the translocation rate up to 40-fold. Furthermore, 3'-end modifications lower or abolish the stimulation by P site-bound tRNA of the GTPase activity of EF-G on the ribosome. The results suggest that a hydrogen-bonding interaction of the 3'-terminal adenine of the leaving tRNA in the E site, most likely base-pairing with 23S rRNA, is essential for the translocation reaction. Furthermore, this interaction stimulates the GTP hydrolyzing activity of EF-G on the ribosome. We propose the following molecular model of translocation: after the binding of EF-G.GTP, the P site-bound tRNA, by a movement of the 3'-terminal single-stranded ACCA tail, establishes an interaction with 23S rRNA in the adjacent E site, thereby initiating the tRNA transfer from the P site to the E site and promoting GTP hydrolysis. The co-operative interaction between the E site and the EF-G binding site, which are distantly located on the 50S ribosomal subunit, is probably mediated by a conformational change of 23S rRNA.     

Modified P Elements That Mimic the P Cytotype in Drosophila Melanogaster

Activity of the P family of transposable elements in Drosophila melanogaster is regulated primarily by a cellular condition known as P cytotype. It has been hypothesized that P cytotype depends on a P element-encoded repressor of transposition and excision. We provide evidence in support of this idea by showing that two modified P elements, each with lesions affecting the fourth transposase exon, mimic most of the P cytotype effects. These elements were identified by means of two sensitive assays capable of detecting repression by a single P element. One assay makes use of cytotype-dependent gene expression of certain P element insertion mutations at the singed bristle locus. The other measures suppression of transposase activity from the unusually stable genomic P element, delta 2-3(99B), that normally produces transposase in both germinal and somatic tissues. The P cytotype-like effects include suppression of snw germline hypermutability, snw somatic mosaicism, pupal lethality, and gonadal dysgenic sterility. Unlike P cytotype, however, there was no reciprocal cross effect in the inheritance of repression.     

High-frequency disruption of the N-myc gene in embryonic stem and pre-B cell lines by homologous recombination.

Identification of gene function has often relied on isolation of mutant cells in which expression of the gene was inactivated. Gene targeting by homologous recombination in tissue culture now may provide a technology to rapidly and directly produce such mutant mammalian cells. We demonstrate that selection of embryonic stem and pre-B cell lines for expression of a promoterless construct containing murine N-myc genomic sequences fused to a gene encoding neomycin resistance allows highly efficient recovery of variants in which the endogenous N-myc gene is disrupted. The high frequency of N-myc gene disruption by this method should permit targeted disruption of both allelic N-myc copies in various cell lines to study N-myc function.