Mechanism of inhibition of RTEM-2 beta-lactamase by cephamycins: relative importance of the 7 alpha-methoxy group and the 3' leaving group

Cefoxitin is a poor substrate of many beta-lactamases, including the RTEM-2 enzyme. Fisher and co-workers [Fisher, J., Belasco, J. G., Khosla, S., & Knowles, J. R. (1980) Biochemistry 19, 2895-2901] showed that the reaction between cefoxitin and RTEM-2 beta-lactamase yielded a moderately stable acyl-enzyme whose hydrolysis was rate-determining to turnover at saturation. The present work shows first that the covalently bound substrate in this acyl-enzyme has a 5-exo-methylene-1,3-thiazine structure, i.e., that the good (carbamoyloxy) 3' leaving group of cefoxitin has been eliminated in formation of the acyl-enzyme. Such an elimination has recently been shown in another case to yield an acyl-beta-lactamase inert to hydrolysis [Faraci, W. S., & Pratt, R. F. (1985) Biochemistry 24, 903-910]. Thus the cefoxitin molecule has two potential sources of beta-lactamase resistance, the 7 alpha-methoxy group and the good 3' leaving group. That the latter is important in the present example is shown by the fact that with analogous substrates where no elimination occurs at the enzyme active site, such as 3'-de(carbamoyloxy)cefoxitin and 3'-decarbamoylcefoxitin, no inert acyl-enzyme accumulates. An analysis of the relevant rate constants shows that the 7 alpha-methoxy group weakens noncovalent binding and slows down both acylation and deacylation rates, but with major effect in the acylation rate, while elimination of the 3' leaving group affects deacylation only.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maternal influence on activity rhythms and reproductive development in Djungarian hamster pups

Photoperiodism and entrainment of the circadian rhythm of locomotor activity were investigated in juvenile Djungarian hamsters. Animals were housed in simulated burrows. Activity was measured as the animal's emergence from a dark nest chamber into an outer box exposed to the room illumination. This burrow emergence activity exhibited marked circadian rhythmicity. Interactions between mother hamsters and their offspring were examined in the simulated burrow system. Male reproductive responses were determined by measuring testicular weights at the time of weaning. It was shown that photoperiodic information received between Days 1 and 15 of life failed to alter the rate of testicular development, but that after Day 15 testicular growth was photoperiod-dependent. The mother, when entrained to a long photoperiod, did not influence the photoperiodic responses of her pups when they were confined to a dark nest box. In contrast, the mother did influence the circadian entrainment patterns of her pups. Pups exhibited a well-developed circadian activity rhythm at weaning with a phase angle roughly similar to that of the mother's activity rhythm. When the maternal rhythms were discrepant with photoperiod information received by the pups directly from the environment, the pups' activity rhythms were synchronized with the light/dark cycle rather than with the rhythm of their mother. Thus, it appears that although pups may first become entrained by maternal cues, they rapidly adjust to the environmental light cycle after leaving the nest.     

In vivo metabolism of inter-alpha-trypsin inhibitor and its proteinase complexes: evidence for proteinase transfer to alpha 2-macroglobulin and alpha 1-proteinase inhibitor

Inter-alpha-trypsin inhibitor was purified by a modification of published procedures which involved fewer steps and resulted in higher yields. The preparation was used to study the clearance of the inhibitor and its complex with trypsin from the plasma of mice and to examine degradation of the inhibitor in vivo. Unlike other plasma proteinase inhibitor-proteinase complexes, inter-alpha-trypsin inhibitor reacted with trypsin did not clear faster than the unreacted inhibitor. Studies using 125I-trypsin provided evidence for the dissociation of complexes of proteinase and inter-alpha-trypsin inhibitor in vivo, followed by rapid removal of proteinase by other plasma proteinase inhibitors, particularly alpha 2-macroglobulin and alpha 1-proteinase inhibitor. Studies in vitro also demonstrated the transfer of trypsin from inter-alpha-trypsin inhibitor to alpha 2-macroglobulin and alpha 1-proteinase inhibitor but at a much slower rate. The clearance of unreacted 125I-inter-alpha-trypsin inhibitor was characterized by a half-life ranging from 30 min to more than 1 h. Murine and human inhibitors exhibited identical behavior. Multiphasic clearance of the inhibitor was not due to degradation, aggregation, or carbohydrate heterogeneity, as shown by competition studies with asialoorosomucoid and macroalbumin, but was probably a result of extravascular distribution or endothelial binding. 125I-inter-alpha-trypsin inhibitor cleared primarily in the liver. Analysis of liver and kidney tissue by gel filtration chromatography and sodium dodecyl sulfate gel electrophoresis showed internalization and limited degradation of 125I-inter-alpha-trypsin inhibitor in these tissues. No evidence for the production of smaller proteinase inhibitors from 125I-inter-alpha-trypsin inhibitor injected intravenously or intraperitoneally was detected, even in casein-induced peritoneal inflammation. No species of molecular weight similar to that of urinary proteinase inhibitors, 19,000-70,000, appeared in plasma, liver, kidney, or urine following injection of inter-alpha-trypsin inhibitor.     

An X-autosome fusion chromosome of Caenorhabditis elegans

Summary The translocation mnT12(IV;X) is a fusion of holocentric chromosomes IV and X, the breakpoints occurring near the left end of IV and the right end of X. Animals homozygous for mnT12 are viable and fertile; they contain five pairs of chromosomes rather than the normal set of six pairs. The mnT12 chromosome is larger than all wild-type chromosomes and thus identifies linkage groups IV and X cytologically. Hermaphrodites heterozygous for mnT12 show high frequency meiotic nondisjunction both between mnT12 and the X chromosome, which results in a high incidence of male self progeny (27% compared to the wild-type incidence of 0.2%), and between mnT12 and chromosome IV, which results in a high incidence of self progeny essentially trisomic for chromosome IV (karyotype IV/mnT12/mnT12). The viability of chromosome IV trisomics has been confirmed by constructing animals trisomic for only normal copies of chromosome IV; these animals are morphologically wild type. Meiotic chromosome disjunction in mnT12 homozygotes appears to be normal, although the frequency of recombination between markers that are normally X-linked is significantly reduced. Males of genotype IV/mnT12/0 are fertile. They can be thought of as having a neo-X(mnT12) neo-Y(normal IV) karyotype since it is possible to maintain a male-hermaphrodite stock of C. elegans consisting of such males and hermaphrodites carrying two neo-X chromosomes and no neo-Y; the organism is thus converted from an XO:XX type of sex determination to an XX:XX system.     

Relationship between probable dominant phosphate compound in soil and phosphorus availability to plants

Summary Surface soil materials from the 0- to 15 cm depth of 12 sites that were suspected to contain high levels of P, as a result of years of repeated applications of either inorganic or organic P fertilizers, were cropped with wheat and alfalfa in the greenhouse for about one year. The total P removed in plant materials provided an estimate of the plant available P in the soils. The probable dominant phosphate compound controlling the release of P in the soil solution during cropping was determined using the GEOCHEM program and an activity diagram. The data show that P availability is partly dependent on the stability of the phosphate compound present, although the relative positions of the points on the activity diagram show no quantitative relationship with either the total plant P uptake or the phosphate buffering capacity of the soils. The positions of the points, however, indicate that with time the formation of more stable P compounds during cropping could be attributed to reactions in the soil as well as to crop removal. The more soluble compounds could have recrystallized or were transformed into compounds of lower solubility. There is also the possibility that the more soluble P compounds were exhausted by crop removal leaving behind the less soluble compounds.     

Identification of a highly conserved domain on phytochrome from angiosperms to algae

A monoclonal antibody (Pea-25) directed to phytochrome from etiolated peas (Pisum sativum L., cv Alaska) binds to an antigenic domain that has been highly conserved throughout evolution. Antigenic cross-reactivity was evaluated by immunoblotting sodium dodecyl sulfate sample buffer extracts prepared from lyophilized tissue samples or freshly harvested algae. Pea-25 immunostained an approximately 120-kilodalton polypeptide from a variety of etiolated and green plant tissues, including both monocotyledons and dicotyledons. Moreover, Pea-25 immunostained a similarly sized polypeptide from the moss Physcomitrella, and from the algae Mougeotia, Mesotaenium, and Chlamydomonas. Because Pea-25 is directed to phytochrome, and because it stains a polypeptide about the size of oat phytochrome, it is likely that Pea-25 is detecting phytochrome in each case. The conserved domain that is recognized by Pea-25 is on the nonchromophore bearing, carboxyl half of phytochrome from etiolated oats. Identification of this highly conserved antigenic domain creates the potential to expand investigations of phytochrome at a cellular and molecular level to organisms, such as Chlamydomonas, that offer unique experimental advantages.     

Identification with Monoclonal Antibodies of a Second Antigenic Domain on Avena Phytochrome that Changes upon Its Photoconversion

An enzyme-linked immunosorbent assay that revealed an antigenic difference between the red-absorbing and far-red-absorbing forms of phytochrome (Pr and Pfr, respectively) near its amino terminus (Cordonnier M-M, H Greppin, LH Pratt 1985 Biochemistry 24: 3246-3253) was used to screen eight additional monoclonal antibodies directed to phytochrome from etiolated oats. While six of these antibodies detected Pr and Pfr with equal affinity, two of them, designated Oat-9 and Oat-16, bound to Pfr 1.6 to 2.3 times better than to Pr. Competitive enzyme-linked immunosorbent assays indicate (a) that Oat-9 and Oat-16 probably bind to the same domain on phytochrome and (b) that this domain is at least 3.5 nanometers away from the epitope near its amino terminus that was shown earlier to change upon phototransformation. Neither the absorbance spectra of Pr and Pfr, nor the rate of dark reversion of Pfr to Pr, was influenced by the presence of Oat-9. Immunoblotting of sodium dodecyl sulfate polyacrylamide gels after electrophoretic separation of phytochrome fragments obtained by endogenous proteolytic digestion indicates that Oat-16 binds to an epitope located on the chromophore half of this chromoprotein. The observation that the epitope recognized by Oat-9 and Oat-16 is also present on at least some of the immunochemically distinct phytochrome that is obtained from green oat shoots (Shimazaki Y, LH Pratt 1985 Planta 164: 333-344), together with the evidence that this epitope undergoes a change upon photoransformation, indicates that it may play an important role in phytochrome function.     

Stable complexes of axoplasmic vesicles and microtubules: protein composition and ATPase activity

Fast transport of axonal vesicles and organelles is a microtubule-associated movement (Griffin, J. W., K. E. Fahnestock, L. Price, and P. N. Hoffman, 1983, J. Neuroscience, 3:557-566; Schnapp, B. J., R. D. Vale, M. P. Sheetz, and T. S. Reese, 1984, Cell, 40:455-462; Allen, R. D., D. G. Weiss, J. H. Hayden, D. T. Brown, H. Fujiwake, and M. Simpson, 1985, J. Cell Biol., 100:1736-1752). Proteins that mediate the interactions of axoplasmic vesicles and microtubules were studied using stable complexes of microtubules and vesicles (MtVC). These complexes formed spontaneously in vitro when taxol-stabilized microtubules were mixed with sonically disrupted axoplasm from the giant axon of the squid Loligo pealei. The isolated MtVCs contain a distinct subset of axoplasmic proteins, and are composed primarily of microtubules and attached membranous vesicles. The MtVC also contains nonmitochondrial ATPase activity. The binding of one high molecular mass polypeptide to the complex is significantly enhanced by ATP or adenyl imidodiphosphate. All of the axoplasmic proteins and ATPase activity that bind to microtubules are found in macromolecular complexes and appear to be vesicle-associated. These data allow the identification of several vesicle-associated proteins of the squid giant axon and suggest that one or more of these polypeptides mediates vesicle binding to microtubules.     

Immunochemical detection with rabbit polyclonal and mouse monoclonal antibodies of different pools of phytochrome from etiolated and green Avena shoots

While two monoclonal antibodies directed to phytochrome from etiolated oat (Avena sativa L.) shoots can precipitate up to about 30% of the photoreversible phytochrome isolated from green oat shoots, most precipitate little or none at all. These results are consistent with a report by J.G. Tokuhisa and P.H. Quail (1983, Plant Physiol. 72, Suppl., 85), according to which polyclonal rabbit antibodies directed to phytochrome from etiolated oat shoots bind only a small fraction of the phytochrome obtained from green oat shoots. The immunoprecipitation data reported here indicate that essentially all phytochrome isolated from green oat shoots is distinct from that obtained from etiolated oat shoots. The data indicate further that phytochrome from green oat shoots might itself be composed of two or more immunochemically distinct populations, each of which is distinct from phytochrome from etiolated shoots. Phytochrome isolated from light-grown, but norflurazon-bleached oat shoots is like that isolated from green oat shoots. When light-grown, green oat seedlings are kept in darkness for 48 h, however, much, if not all, of the phytochrome that reaccumulates is like that from etiolated oat shoots. Neither modification during purification from green oat shoots of phytochrome like that from etiolated oat shoots, nor non-specific interference by substances in extracts of green oat shoots, can explain the inability of antibodies to recognize phytochrome isolated from green oat shoots. Immunopurified polyclonal rabbit antibodies to phytochrome from etiolated pea (Pisum sativum L.). shoots precipitate more than 95% of the photoreversible phytochrome obtained from etiolated pea shoots, while no more than 75% of the pigment is precipitated when phytochrome is isolated from green pea shoots. These data indicate in preliminary fashion that an immunochemically unique pool of phytochrome might also be present in extracts of green pea shoots.Abbreviation ELISA enzyme-linked immunosorbent assay - mU milliunit - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome     

Export of species to islands from sources of differing maturity

Export of species from sources (epicenters) of differing ages and complexities was examined using laboratory microcosms. Polyurethane foam (PF) artificial substrates were colonized by protozoans for different time periods in a small pond. Substrates were returned to the laboratory and used as epicenters for protozoan colonization of barren PF islands in initially sterile microcosms. Islands were exposed to epicenters for either 24 h or continuously for 28 d. Islands from pairs of microcosms exposed to epicenters of identical ages were sampled on 1, 3, 7, 14, 21, 28 and 46 d after initial epicenter exposure. Colonization parameters were estimated by fitting numbers of colonizing species to the MacArthur-Wilson equilibrium model. Islands exposed continuously to epicenters were colonized by significantly more species than those exposed for only 24 h. Islands exposed to immature, species poor epicenters were colonized by a greater proportion of the source community than those exposed to more mature, species rich epicenters. All islands were depauperate compared to epicenters except those exposed to the most immature (1 d old) epicenter. Colonization continued at a reduced rate in spite of the absence of the epicenter. Results from communities with rapid species turnover and rapidly reproducing species suggest that the continuous presence of a species source is less important for colonization of a new habitat. Dispersal of potential colonists occurs rapidly in these communities. Less mature communities dominated by pioneer forms are more effective at producing colonists than more mature communities.