Affinity labeling of stellacyanin by Cr(II) aquo ions

Stellacyanin, the single blue copper protein from $\text{Rhus}$$\text{vernicifera}$, is reduced stoichiometrically by Cr(II)_aq ions yielding a 1:1 adduct between the Cr(III) produced and the reduced protein. This Cr(III)-labeled stellacyanin is substitution inert and no significant loss of the label occurs during extensive dialysis for more than a week. Oxidation by O₂ of the Cr(III)-labeled Cu(I) stellacyanin does not cause the loss of Cr(III) either. Furthermore, reduction of the Cr(III)-labeled stellacyanin Cu(II) by a second equivalent of Cr(II) may be attained without any further labeling. Thus, the one mole of Cr ions binds to stellacyanin during the first reduction step and is most probably coordinated at a specific locus on that protein.     

Effect of metal binding on the intrinsic fluorescence of bovine carbonic anhydrase

Bovine carbonic anhydrase shows an intrinsic fluorescence which results from tryptophans located in different microenvironments. It is possible to attribute the whole fluorescence to at least two types of tryptophan.This fluorescence is differently affected by the binding of different metals. In fact while Zn²⁺ causes an increase of the fluorescence yield, the binding of Co²⁺, Cu²⁺ and Hg²⁺ is followed by a quenching of the fluorescence. The quenching is about 40% for the cobalt, 80% for the copper and 60% for the mercury derivative. The binding of Cu²⁺ and Hg²⁺ induces also a change in the shape of the fluorescence emission spectrum. This fact suggests a different influence of the metals on the various types of tryptophan.The fluorescence quenching induced by iodide which can bind to the metal and act as a fluorescence perturbing agent is also indicative of the presence of different tryptophans.     

A quick method for testing recessive lethal damage with a diploid strain of Aspergillus nidulans.

A simple method capable of detecting recessive lethal damage in a diploid strain of Aspergillus nidulans is described. The method scores the recessive lethals on the 1st, the 3rd and the 5th chromosomes, which represent about 40% of the total map of A. nidulans. Two examples of induced lethals, with ultraviolet irradiation and methyl methanesulfonate are shown. The frequency of lethals may reach 36% of the total population with UV irradiation.     

Deregulation of immunoglobulin expression: Is this the main cause of Burkitt's lymphoma?

We here examine the role of c-myc in the aetiology of Burkitt's lymphomas. We suggest that c-myc causes cellular clones to become immortal while the deregulation of cell multiplication is the consequence of an altered production and/or structure of immunoglobulin chains caused by the 8-14, 8-2 or 8-22 translocations. Data relative to other immunoproliferative disorders are consistent with the hypothesis that the immunoglobulins play a key role in the regulation of the multiplication of lymphocytic cells.     

Full, reversible copper removal from ascorbate oxidase

Anaerobic treatment with cyanide of reduced ascorbate oxidase causes total depletion of copper. No significant amount of the metal is reincorporated when the apo-enzyme is incubated with cupric ions, but it is upon incubation with a stoichiometric amount (eight mol per mol of native enzyme) of a Cu(I) complex stable in air [Cu(I)(thiourea)3]Cl. The yield in reconstituted protein is higher under anaerobic conditions (85-90%) than in air (70-75%). By treatment with less than stoichiometric amounts of [Cu(I)(thiourea)3]Cl the apo-protein binds copper preferentially at the blue copper site. As a consequence the recovery of enzymatic activity is percentually lower than copper reincorporation.     

Mitotic intragenic recombination as a consequence of heteroduplex formation in Aspergillus nidulans

Summary A diploid strain of Aspergillus nidulans with two heteroallelic mutations in the pabaA cistron (right arm of the first chromosome) has been studied. Part of the paba-independent colonies which have been examined was heterogeneous, i.e. they showed conidia of different colour and genotype. The genetic analysis of the various type of these heterogeneous colonies leads to the conclusion that, in Aspergillus nidulans, mitotic intragenic recombination is, in most cases, consequence of a single-strand break and exchange followed by the formation of a very long hybrid-DNA region (in our case a maximum of 22 meiotic units); the selected characteristics arise mainly by gene-conversion.Furthermore, data show a high negative interference between the selected crossing-over and a second crossing-over on the left arm and probably also on different chromosomes. The latter exchange occurs, as the former, between subchromatidic units.