STUDIES ON THE ORIGIN OF RIBOSOMES IN AMOEBA PROTEUS

The origin of cytoplasmic RNA and ribosomes was studied in Amoeba proteus by transplantation of a radioactive nucleus into an unlabeled cell followed by examination of the cytoplasm of the recipient for the presence of label. When a RNA-labeled nucleus was used, label appeared in the ribosomes, ribosomal RNA, and soluble RNA. Since the kinetics of appearance of labeled RNA indicates that the nucleus was not injured during the transfer, and since the transferred nuclear pool of labeled acid-soluble RNA precursors is inadequate to account for the amount of cytoplasmic RNA label, it is concluded that cytoplasmic ribosomal RNA is derived from acid-insoluble nuclear RNA and is probably transported as an intact molecule. Likewise, cytoplasmic soluble RNA probably originated in the nucleus, although labeling by terminal exchange in the cytoplasm is also possible. The results were completely different when a protein-labeled nucleus was grafted into an unlabeled host. In this case, label was found only in soluble proteins in the host cell cytoplasm, and there were no (or very few) radioactive ribosomes. This suggests that the nuclear pool of ribosomal protein and ribosomal protein precursors is relatively small and perhaps nonexistent (and, furthermore, shows that there was no cytoplasmic ribosomal contamination of the transferred nucleus).     

In Vitro Susceptibility of Neisseria gonorrhoeae to Nine Antimicrobial Agents

The in vitro action of nine antibiotics was tested by the agar streak method against 45 gonococcal strains isolated from penicillin-therapy failures. The penicillin susceptibility range of these strains was 0.003 to 1.32 μg/ml, and the tetracycline susceptibility range was 0.125 to 2.0 μg/ml. Minimal inhibitory concentrations of minocycline and doxycycline paralleled the activity of tetracycline and ranged from 0.125 to 1.0 μg/ml and 0.125 to 2.0 μg/ml, respectively. Rifampicin, with a narrow range of 0.5 to 1.0 μg/ml, inhibited 75% of the strains at 0.5 μg/ml. The range for cephaloridine and cephaloglycine was 0.5 to 20.0 μg/ml, but another cephalosporium derivative, cephalexin, exhibited greater activity in its range of 0.25 to 20.0 μg/ml. A semisynthetic penicillin, carbenicillin, with a range of 0.025 to 0.75 μg/ml, displayed more activity against the lower susceptible penicillin G gonococcal strains.     

SEROLOGICAL STUDIES IN BAPTISIA AND CERTAIN OTHER GENERA OF THE LEGUMINOSAE

Fourteen species of Baptisia were compared serologically, using antiserum against B. nuttalliana. By means of both immunoelectrophoretic and double-diffusion techniques, it was possible to disclose 11 distinct arcs plus some weaker arcs, with few reliable (definite and repeatable) differences detected among the species of Baptisia investigated. Since the individual species of Baptisia are often quite distinctive, as judged by other chemical and morphological criteria, the serological data are in this instance conservative and appear to be effective in circumscribing the genus. In contrast, striking interspecific differences in the serological properties of unicellular green algae have been obtained (reported elsewhere) by similar techniques in this laboratory. It is concluded that serological data should be regarded as adjuncts to other systematic knowledge only on the basis of empirical manifestations of their utility. There is no clear justification for regarding serological data as intrinsically either superior or inferior to other systematic criteria.     

Electron microscopy of resorbing surfaces of dental hard tissues

Summary The resorbing surfaces of exfoliated or extracted human deciduous molar teeth were studied directly in the scanning electron microscope and indirectly by a single stage carbon replica technique for the transmission electron microscope. Some specimens of resorbing bone were also examined. Some of the material was examined after a simple washing process and some after removal of the organic matrix with hot 12 diamino ethane.The typical crossbanding of collagen could be seen on resorbing cement and dentine surfaces. This is taken as an indication that demineralisation is the first step in resorption. The very highly mineralised peritubular dentine remained proud of the resorbing surfaces thus indicating that its mineral component is in some way selectively protected.Enamel prism sheaths were also found to be selectively resistant to resorption and this is assumed to be related to the protection of the mineral component in these regions by their higher and/or different organic content. No prism sheaths were found next to the enamel-dentine junction and there was only a slight step down from the enamel to the dentine.Large remineralization crystals were found located at the borders between adjacent Howship's lacunae.The natural resorbing surfaces were compared with surfaces subjected to purely physical erosion by 5 keV argon ion beam bombardment (Boyde and Stewart, 1962).Our thanks are due to Mr. A.D.G. Stewart for permission to publish Fig. 5, which was prepared by him. The Cambridge Instrument Company Stereoscan scanning electron microscope was provided by the (U. K.) Science Research Council.     

Ligand-induced conformational changes in cytosolic protein kinase C

The changes in intrinsic spectral properties of protein kinase C were monitored upon association with its divalent cation and lipid activators in a model membrane system. The enzyme demonstrated changes in both its intrinsic fluorescence and far ultraviolet circular dichroism spectra upon association with lipid vesicles in the absence of calcium. The acidic phospholipid, phosphatidylserine, significantly quenched the intrinsic tryptophan fluorescence and was also the most potent lipid support for the phosphorylating activity of the enzyme. The enzyme was fully activated by a number of Ca2(+)-lipid combinations which correlated with maximal fluorescence quenching (40-50%) of available tryptophan residues in hydrophobic domains. The circular dichroism structure of the associated active-protein Ca2(+)-lipid complexes suggested different active enzyme secondary structures. However, the Ca2(+)-dependent changes in fluorescence and circular dichroism spectra were observed only after the enzyme associated with the lipid vesicles. These data suggest that protein kinase C has the properties of a complex multidomain protein and provides an additional perspective into the mechanism of protein kinase C activation.     

Spatial distribution and seasonal changes in methylmercury concentrations in shallow lakes

The environmental factors governing the distribution and behaviour of total and methylmercury within mercury contaminated shallow lakes, associated with the River Yare, Norfolk, UK, have been assessed in situ through the use of sediment cores. These were analysed for microbial and chemical changes on both a temporal and spatial scale. The distribution of total mercury proved to be site dependent and related to the hydrology, sediment transport dynamics, the degree of sediment disturbance and distance from the contamination source. The core profiles revealed a subsurface peak in total mercury with maximum concentrations residing at depths of 12 and 36 cm, depending upon location, with enrichment extending down to depths in excess of 88 cm. This vertical distribution was deemed to reflect historical emission in the late 1960s and early 1970s rather than post depositional migration effects. The distribution of methylmercury was distinct from that of its inorganic counterpart since it also displayed temporal variability with highest concentrations occurring in the spring and summer. Maximum concentrations also prevailed in the uppermost 12 cm of sediment, with peak loadings at or just below the sediment/water interface and detectable levels being restricted to the upper 36 cm. The temporal and spatial behaviour of methylmercury appeared to reflect variations in redox potential, the availability of the Hg²⁺ ion and the nature of microbial populations.     

Gamma-ray-induced changes in hypodermal mesocarp tissue plasma membrane of pre- and post-storage muskmelon

Gamma irradiation (1.0 kGy) of intact, newly harvested, mature muskmelon fruit (Cucumis melo L. var. reticulatus Naud.) appears to have an immediate deleterious effect, but also a long-term beneficial effect, on the integrity and function of the plasma membrane (PM) of hypodermal mesocarp tissue. The initial consequences of gamma irradiation included an increase in the free sterol:phospholipid ratio, resulting at least in part from deglycosylation of steryl glycosides, a decrease in the spinasterol:7-stigmastenol ratio in each of the PM steryl lipids (free sterols, steryl glycosides, and acylated steryl glycosides), and a decrease in H⁺-ATPase activity. Irradiation did not increase protein loss, suggesting that the decrease in H⁺-ATPase activity resulted from either direct inactivation of the enzyme or altered PM ordering caused by the steryl lipid modifications. The long-term beneficial effects of irradiation, observed following 10 days of commercial storage, included greater retention of total PM protein, a diminished decline in total PM phospholipids (PL) and in the PL:protein ratio, and maintenance of greater overall H⁺-ATPase activity (activity was the same as in controls on a per mg protein basis, but there was > 30% more protein in the PM of stored irradiated fruit). These results indicate that 1 kGy gamma irradiation administered prior to storage slowes the progression of two key parameters of senescence, PM protein loss and PL catabolism.