Cellular and extracellular siderophores of Aspergillus nidulans and Penicillium chrysogenum.

Aspergillus nidulans and Penicillium chrysogenum produce specific cellular siderophores in addition to the well-known siderophores of the culture medium. Since this was found previously in Neurospora crassa, it is probably generally true for filamentous ascomycetes. The cellular siderophore of A. nidulans is ferricrocin; that of P. chrysogenum is ferrichrome. A. nidulans also contains triacetylfusigen, a siderophore without apparent biological activity. Conidia of both species lose siderophores at high salt concentrations and become siderophore dependent. This has also been found in N. crassa, where lowering of the water activity has been shown to be the causal factor. We used an assay procedure based on this dependency to reexamine the extracellular siderophores of these species. During rapid mycelial growth, both A. nidulans and P. chrysogenum produced two highly active, unidentified siderophores which were later replaced by a less active or inactive product--coprogen in the case of P. chrysogenum and triacetylfusigen in the case of A. nidulans. N. crassa secreted coprogen only. Fungal siderophore metabolism is varied and complex.     

Continuous open flow-through system as a model for oil degradation in the arctic ocean

A continuous flow-through system incubated in situ was used to model oil biodegradation in Arctic coastal waters. High numbers of oil-degrading microorganisms were found in the Arctic coastal waters examined in this study. The microbial community underlying oil slicks increased and showed a population shift to a greater percentage of hydrocarbon-utilizing microorganisms. Microbial populations and oil biodegradation were increased by the addition of nitrogen and phosphorus. Both abiotic and biodegradative losses were lower than expected, perhaps due to the unusually harsh, ice-dominated Arctic summer, during which these tests were conducted. Chromatographic and spectrometric analyses showed that residual oils contained similar percentages of individual components and classes of hydrocarbons, regardless of the amount of degradation, indicating that most components of the oil were being degraded at similar rates.     

3H-Spiroperidol binding and dopamine-stimulated adenylate cyclase: evidence for multiple classes of receptors in primate brain regions.

Studies of displacement by agonist and antagonist drugs of ³H-spiroperidol binding in brain regions of $\text{Cebus}$ and rhesus monkeys revealed one type of receptor in caudate nucleus and a second type of receptor in both frontal and anterior limbic cortex. Compared with caudate, the cortical regions were more sensitive to clozapine and loxapine, equally sensitive to fluphenazine and relatively less sensitive to haloperidol. Also, the cortical regions were insensitive to molindone. Parallel studies using the dopamine-stimulated adenylate cyclase have demonstrated three types of receptors, one in caudate, a second in frontal cortex, and a third in anterior limbic cortex. In each region studied, relative sensitivities to drug using these two methods differed, suggesting that in each of these regions only a relatively small portion of ³H-spiroperidol receptors are coupled to adenylate cyclase.     

Electron microscopic evidence for splicing of SV40 late mRNAs.

Poly(A)-containing SV40 cytoplasmic RNA was hybridized with linear double-stranded SV40 DNA and formed RNA displacement loops (R loops). The structures visualized in the electron microscope are consistent with the conclusion that the leader sequences at the 5' ends of the 16S and 19S late mRNAs are not coded immediately adjacent to the main portions of the mRNAs. These data are consistent with either segmentation of the leaders or heterogeneity of their lengths. Measurements carried out on the R loop structures have provided the locations, on the physical map of SV40 DNA, for the bodies and leaders of the 16S and 19S late mRNAs, and the lengths of the bodies, leaders and the corresponding intervening DNA sequences.     

Unassisted refolding of urea unfolded rhodanese

In vitro refolding after urea unfolding of the enzyme rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) normally requires the assistance of detergents or chaperonin proteins. No efficient, unassisted, reversible unfolding/folding transition has been demonstrated to date. The detergents or the chaperonin proteins have been proposed to stabilize folding intermediates that kinetically limit folding by aggregating. Based on this hypothesis, we have investigated a number of experimental conditions and have developed a protocol for refolding, without assistants, that gives evidence of a reversible unfolding transition and leads to greater than 80% recovery of native enzyme. In addition to low protein concentration (10 micrograms/ml), low temperatures are required to maximize refolding. Otherwise optimal conditions give less than 10% refolding at 37 degrees C, whereas at 10 degrees C the recovery approaches 80%. The unfolding/refolding phases of the transition curves are most similar in the region of the transition, and refolding yields are significantly reduced when unfolded rhodanese is diluted to low urea concentrations, rather than to concentrations near the transition region. This is consistent with the formation of "sticky" intermediates that can remain soluble close to the transition region. Apparently, nonnative structures, e.g. aggregates, can form rapidly at low denaturant concentrations, and their subsequent conversion to the native structure is slow.     

Expression of cloned bovine adrenal rhodanese

A cDNA for the enzyme rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) has been cloned from a bovine adrenal library. An initiator methionine codon precedes the amino-terminal amino acid found in the isolated protein. Rhodanese is synthesized in the cytoplasm and transferred to the mitochondrial matrix. Thus, any amino-terminal sequence required for organelle import is retained in the mature protein. Furthermore, the DNA sequence shows that there are three additional amino acids, Gly-Lys-Ala, at the carboxyl terminus that are not found by protein sequencing. Additionally, comparison of the published amino acid sequence with that encoded by the open reading frame revealed three differences in the amino acid sequence. Comparison of the bovine and chicken liver sequences shows an overall level of 70% sequence homology, but there is complete identity of all residues that have been implicated in the function of the enzyme. When two mammalian cells, cos-7 and 293 cells, were transiently transfected with a plasmid containing the rhodanese coding region, rhodanese activity in lysates increased approximately 20-fold. Fluorograms of denaturing polyacrylamide gels detected a large increase in a polypeptide that co-migrated with the native protein and reacted with anti-rhodanese antibodies. Nondenaturing gels showed two active species that co-migrated with the two major electrophoretic forms purified by current procedures. Escherichia coli, transformed with a plasmid containing the rhodanese coding region, showed a 15-fold increase in rhodanese activity over baseline values. When the E. coli recombinant protein was analyzed on a nondenaturing gel, only one species was observed that co-electrophoresed with the more electropositive variant seen in purified bovine liver rhodanese. This single variant could be converted by carboxypeptidase B digestion to a form of the enzyme that co-migrated with the more electronegative species isolated from bovine liver. Thus, two major, enzymatically active electrophoretic variants, commonly observed in mammalian cells, can be accounted for by carboxyl-terminal processing without recourse to other post-translational modifications.     

Purification of bovine liver rhodanese by low-pH column chromatography

We report a purification of bovine liver rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) using column chromatography under conditions that take advantage of recent information regarding the structure and stability of this enzyme. At low pH (e.g., pH 4-6), rhodanese is stabilized against inactivation processes. By maintaining rhodanese at low pH, column chromatography, and especially ion-exchange chromatography, becomes practical, without loss of enzymatic activity. A purification method involving the sequential use of cation-exchange, size-exclusion, and hydrophobic-interaction chromatography was developed, and rhodanese was purified with good yield to electrophoretic purity and high specific activity. Previous methods for purifying bovine liver rhodanese employ repeated ammonium sulfate fractionations and crystallization of the rhodanese. In these methods, it is difficult to separate rhodanese from yellow-brown contaminants in the final stages of the procedures. Here, yellow-brown contaminants, which copurify with rhodanese on the first two columns, are completely resolved by hydrophobic interaction chromatography. This method can be readily scaled up, requires no special equipment, eliminates the variability inherent in previous methods, and is less dependent upon experience.     

Reducing sugars can induce the oxidative inactivation of rhodanese.

The enzyme rhodanese (thiosulfate sulfurtransferase, EC 2.8.1.1) is inactivated on incubation with reducing sugars such as glucose, mannose, or fructose, but is stable with non-reducing sugars or related polyhydroxy compounds. The enzyme is inactivated with (ES) or without (E) the transferable sulfur atom, although E is considerably more sensitive, and inactivation is accentuated by cyanide. Inactivation of E is accompanied by increased proteolytic susceptibility, a decreased sulfhydryl titer, a red-shift and quenching of the protein fluorescence, and the appearance of hydrophobic surfaces. Superoxide dismutase and/or catalase protect rhodanese. Inactive enzyme can be partially reactivated during assay and almost completely reactivated by incubation with thiosulfate, lauryl maltoside, and 2-mercaptoethanol. These results are similar to those observed when rhodanese is inactivated by hydrogen peroxide. These observations, as well as the cyanide-dependent, oxidative inactivation by phenylglyoxal, are explained by invoking the formation of reactive oxygen species such as superoxide or hydrogen peroxide from autooxidation of alpha-hydroxy carbonyl compounds, which can be facilitated by cyanide.     

Micelle-assisted protein folding. Denatured rhodanese binding to cardiolipin-containing lauryl maltoside micelles results in slower refolding kinetics but greater enzyme reactivation.

Unfolded (inactive) rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) can be reactivated in the presence of detergents, e.g. lauryl maltoside (LM). Here, we report the reactivation of urea-unfolded rhodanese in the presence of mixed micelles containing LM and the anionic mitochondrial phospholipid, cardiolipin (CL). Reactivation times increased as the number of CL molecules/micelle was increased. A maximum of 94% of the activity was recovered at 2.2 CL/micelle. Only 71% of the activity was recovered in the absence of CL. The major zwitterionic mitochondrial phospholipid, phosphatidylcholine (PC), had no effect on the LM-assisted reactivation of rhodanese. Size exclusion chromatography showed that denatured, but not native, rhodanese apparently binds to micellar amounts of LM and CL/LM, but not to PC/LM micelles. The lifetime of the enzyme-micelle complex increased with the number of CL molecules/micelle. Furthermore, chromatographic fractions containing micelle-bound enzyme had no activity, while renatured rhodanese-containing fractions were active. These results suggest that transient complexes form between enzyme and both LM and CL/LM micelles, and that this complex formation may be necessary for reactivation. For CL/LM micelles, interactions may occur between the positively charged amino-terminal sequence of rhodanese and the negatively charged CL phosphate. Finally, this work shows that there are similarities between "micelle-assisted" and chaperonin-assisted rhodanese refolding.     

Effect of small release on force during sarcomere-isometric tetani in frog muscle fibers.

We investigated the effect of small shortening imposed on frog muscle fibers during sarcomere-isometric tetani. Sarcomere length was initially kept constant, then slightly shortened (1%-5% of initial length) and clamped again for the remainder of the tetanus. Force level after the shortening was higher than the force level preceding the release. The size of the increase was larger than that predicted by the descending limb of the linear force-length relation. The difference between measured and predicted force levels increased with sarcomere length. At a sarcomere length of 3.2 microns, the force level after the shortening was higher by 50% than the force level expected from the linear descending limb. Dispersion of sarcomere-length within the sampled region was measured by two independent methods: striation imaging and analysis of the intensity profile of the first diffraction order. Sarcomere-length inhomogeneity in the sampled region was too small (standard deviation from the average sarcomere-length was +/- 0.03 microns) to account for the size of the increase in force. We studied the dependence of increase in tetanic force level after small sarcomere-length release on the size, velocity and timing of the release, as well as on initial sarcomere-length. Release size was the major determinant of the amount of increase in force. Release of 20 nm per half sarcomere was sufficient to produce an almost full force increase. Larger releases increased the force only moderately. Over the range studied, release velocity and timing had little or no effect.