The purification and characterization of arginase from Saccharomyces cerevisiae

In Saccharomyces cerevisiae, ornithine transcarbamoylase and arginase form a regulatory multienzyme complex (Hensley, P. (1988) Curr. Top. Cell. Regul. 29, 35-75). In this complex, arginase acts as a negative allosteric effector for ornithine transcarbamoylase. Before an analysis of the factors which promote and stabilize complex formation, arginase was purified in milligram quantities from a plasmid-containing, enzyme-overproducing, protease-deficient yeast strain and its physical characterization undertaken. The purified enzyme has a specific activity of 885 mumol urea min-1 mg-1 and a Km for arginine of 15.7 mM. The ultraviolet spectrum has a maximum absorbance at 279 nm, and the steady-state fluorescence emission spectrum has a maximum intensity at 337 nm, suggesting that the 3 tryptophans/polypeptide chain are in a relatively hydrophobic environment. Arginase has a weakly bound manganese responsible for the maintenance of the catalytic activity and is known to be heat activated in the presence of manganese. This effect is half-maximal at 12.1 microM manganese. In addition to a catalytic requirement for manganese, the presence of a more tightly bound metal is suggested from sedimentation studies. The native trimeric enzyme has a sedimentation coefficient of 5.95 S. Removal of the weakly associated metal results in no change in the sedimentation coefficient. However, dialysis with EDTA causes the s-value to decrease to 4.65 S, suggesting that under these conditions, the trimeric enzyme may partially dissociate. An analysis of CD spectra shows that significant spectral changes result from the removal of both the weakly bound metal and dialysis against EDTA.     

The Altyerre Story—‘Suffering Badly by Translation’

In culture‐contact situations, it is commonplace for words to be borrowed from other unrelated vernaculars, for their pronunciations to be changed, and their meanings modified to fit new contexts. The Arandic word altyerre is a rather extreme example of this, and at the end of the nineteenth century, the ‘translation’ of the related word Alcheringa as ‘dream‐times’ sparked a debate that, in some forms, continues to this day. In this article, I discuss some of the reasons why this particular word struck such a controversial chord. I give an updated semantic perspective on the word altyerre , drawing on evidence from Arandic languages and from other languages in Central Australia. Then I examine some of the consequences of both religious and secular interpretations of altyerre and show how the popularisation of this word and its translations has impacted on its meanings in current usage.     

The temperate-tropical gradient of planktonic Protozoa and Rotifera

Many flagellates, ciliates and rhizopods appear to be cosmopolitan, at least when considered at the morphospecies level. There are indications of tropical endemics among the ciliates and the rhizopods, but the percentage of endemics appears to be low. Among the rotifers there is a well marked latitudinal gradient, but the picture is complicated by the occurrence of warm water species during hot summers in temperate regions. A further complication has been introduced by the artificial development of heated water associated with power stations. The characteristic rotifer associations of the tropics are governed largely by temperature and salinity. A study of the altitudinal distribution of rotifers in Africa reveals an interplay between latitude and altitude in determining the similarities of the associations to those found in the temperate Old World.     

Reducing the concentration of selected marker improves efficiency of cotransfer of unselected DNA into SV40-transformed human fibroblasts.

A substantial increase in transfer of unselected DNA to two human SV40-transformed fibroblast cell lines was obtained by reducing the concentration of the cotransferred selected marker DNA. The average amount of unselected DNA transferred, even under favorable conditions, was still low compared to that reported for some rodent cell lines. Our results suggest that in human fibroblasts there is strong competition between exogenous DNA molecules for integration and maintenance, and that more unselected DNA is retained in the presence of only one copy of the selected marker.     

Binding of correolide to K(v)1 family potassium channels. Mapping the domains of high affinity interaction.

Correolide, a novel nortriterpene natural product, potently inhibits the voltage-gated potassium channel, K(v)1.3, and [(3)H]dihydrocorreolide (diTC) binds with high affinity (K(d) approximately 10 nM) to membranes from Chinese hamster ovary cells that express K(v)1.3 (Felix, J. P., Bugianesi, R. M., Schmalhofer, W. A., Borris, R., Goetz, M. A., Hensens, O. D., Bao, J.-M., Kayser, F. , Parsons, W. H., Rupprecht, K., Garcia, M. L., Kaczorowski, G. J., and Slaughter, R. S. (1999) Biochemistry 38, 4922-4930). Mutagenesis studies were used to localize the diTC binding site and to design a high affinity receptor in the diTC-insensitive channel, K(v)3.2. Transferring the pore from K(v)1.3 to K(v)3.2 produces a chimera that binds peptidyl inhibitors of K(v)1.3 with high affinity, but not diTC. Transfer of the S(5) region of K(v)1.3 to K(v)3.2 reconstitutes diTC binding at 4-fold lower affinity as compared with K(v)1.3, whereas transfer of the entire S(5)-S(6) domain results in a normal K(v)1.3 phenotype. Substitutions in S(5)-S(6) of K(v)1.3 with nonconserved residues from K(v)3.2 has identified two positions in S(5) and one in S(6) that cause significant alterations in diTC binding. High affinity diTC binding can be conferred to K(v)3.2 after substitution of these three residues with the corresponding amino acids found in K(v)1.3. These results suggest that lack of sensitivity of K(v)3.2 to diTC is a consequence of the presence of Phe(382) and Ile(387) in S(5), and Met(458) in S(6). Inspection of K(v)1.1-1.6 channels indicates that they all possess identical S(5) and S(6) domains. As expected, diTC binds with high affinity (K(d) values 7-21 nM) to each of these homotetrameric channels. However, the kinetics of binding are fastest with K(v)1.3 and K(v)1.4, suggesting that conformations associated with C-type inactivation will facilitate entry and exit of diTC at its binding site. Taken together, these findings identify K(v)1 channel regions necessary for high affinity diTC binding, as well as, reveal a channel conformation that markedly influences the rate of binding of this ligand.