Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Microspectrophotometry”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1991

Ultraviolet photoreception in carp: microspectrophotometry and behaviorally determined action spectra.

This study demonstrates correlations between u.v. sensitivity and microspectrophotometric absorption spectra determined sequentially for the same group of individuals. We used the heart-rate conditioning technique to measure spectral sensitivity of carp, a species known to have u.v.-sensitive photoreceptors. Mean spectral sensitivity (n = 3) determined with a spectrally-broad background (450 nm long pass filter) revealed a small but consistent u.v. peak (lambda max of 380 nm) in addition to the other long wavelength peaks. An intense blue-green background (490 nm) produced a more prominent u.v. peak (lambda max of 400 nm) when a 450 nm longpass filter was added to the background. Microspectrophotometric measurements of u.v.-sensitive photoreceptors from one individual, which belonged to the group used in the spectral sensitivity experiments, revealed an average lambda max of 377.5 nm (SD +/- 4.5 nm, n = 5 cells). Bleaching and dichroic measurements of these receptors ensured that we were examining typical vertebrate visual pigments and not stable photoproducts. The mean spectral sensitivity points were compared with the u.v. and blue-sensitive visual pigment absorption spectra. A linear subtractive model and ocular media absorption were used in this comparison for the various photic conditions used in the heart-rate conditioning experiments. The model successfully described the sensitivity of the test fish in two cases but in a third case there was some discrepancy. The model generated curve was broader than the spectral sensitivity of the u.v.-sensitive cone mechanism on the shortwave side even though the ocular media corrections had been accounted for.

Animals↗
PubMed1999

Visual pigments and oil droplets in the retina of a passerine bird, the canary Serinus canaria: microspectrophotometry and opsin sequences.

The visual receptors of the passeriform bird Serinus canaria, the canary, have been examined microspectrophotometrically and the sequences of the opsins determined. Rods have a maximum absorbance (lambda max) at 506 nm. Four spectral classes of single cone are present: long-wave-sensitive (LWS) containing a photopigment with lambda max at 569 nm, middle-wave-sensitive (MWS) with lambda max at 505 nm, short-wave-sensitive (SWS) with lambda max at 442 nm, and ultraviolet-sensitive (UVS) with lambda max at about 366 nm. Double cones possess the 569-nm pigment in both members. Typical combinations of photopigment and oil droplet occur in most cone classes. An ambiguity exists in the oil droplet of the single LWS cones. In some birds, LWS cones are paired with an R-type droplet, whereas in the majority of canaries the LWS pigment is paired with a droplet similar to the P-type of double cones. Mechanisms of spectral tuning within each opsin class are discussed.

Animals↗
PubMed1998

Cryocrystallography and microspectrophotometry of a mutant (alpha D60N) tryptophan synthase alpha 2 beta 2 complex reveals allosteric roles of alpha Asp60.

We have investigated the role of Asp60 of the alpha-subunit in allosteric communication between the tryptophan synthase alpha- and beta-subunits. Crystallographic and microspectrophotometric studies have been carried out on a mutant (alpha D60N) tryptophan synthase alpha 2 beta 2 complex which has no observable alpha-activity, but has substantial beta-activity. Single-crystal polarized absorption spectra indicate that the external aldimine is the predominant L-serine intermediate and that the amount of the intermediate formed is independent of pH, monovalent cations, and allosteric effectors. The three-dimensional structure is reported for this mutant enzyme complexed with indole 3-propanol phosphate bound to the alpha-site and L-serine bound to the beta-site (alpha D60N-IPP-Ser), and this structure is compared with that of the unliganded mutant enzyme (alpha D60N). In the complex, L-serine forms a stable external aldimine with the pyridoxal phosphate coenzyme at the active site of the beta-subunit. The conformation of the unliganded mutant is almost identical to that of the wild type enzyme. However, the structure of the mutant complexed with IPP and serine exhibits ligand-induced conformational changes much smaller than those observed previously for another mutant enzyme in the presence of the same ligands (beta K87T-IPP-Ser) [Rhee, S., Parris, K. D., Hyde, C. C., Ahmed, S. A., Miles, E. W., and Davies, D. R. (1997) Biochemistry 36, 7664-7680]. The alpha D60N-IPP-Ser alpha 2 beta 2 complex does not undergo the following ligand-induced conformational changes: (1) the closure of the alpha-subunit loop 6 (residues 178-191), (2) the movement of the mobile subdomain (residues 93-189) of the beta-subunit, and (3) the rotation of the alpha-subunit relative to the beta-subunit. These observations show that alpha Asp60 plays important roles in the closure of loop 6 and in allosteric communication between the alpha- and beta-subunits.

Allosteric Regulation↗
PubMed1957

Microspectrophotometry of cell nuclei stained with the Feulgen reaction. IV. Formation of tetraploid nuclei in rat liver cells during postnatal growth.

1. DNA contents of the individual parenchymal nuclei of rat livers during postnatal growth were estimated by microspectrophotometric apparatus, and different ploidy classes of nuclei were classified by their DNA contents. With the same material the total number of parenchymal nuclei in the liver was counted microscopically. 2. If the DNA content of nuclei encountered most frequently in several tissues represents the diploid class, the ploidy classes of the rat liver cell nuclei correspond to di-, tri-, tetra-, and octoploid, with the di- and tetraploid ones predominating considerably. 3. In suckling rats (below 25 gm. of body weight) the liver parenchyma is composed almost exclusively of cells with diploid nuclei, whereas in young rats (above 80 gm.), of tetraploid nuclei. In the growth stage between 25 and 80 gm., there is a remarkable replacement of the diploid nuclei by the tetraploid ones. However, in the liver of adult rats weighing more than 150 gm., any increase or decrease in the frequency of diploid and tetraploid nuclei is hardly observable. In such rats, the nuclear population of the liver parenchyma seems to reach a cell-ecological equilibrium which is considered to be a stable one. 4. It is shown that such nuclear populations and the total number of nuclei in a liver are controlled by the growth state, and not by the age. 5. The decrease in the total number of diploid nuclei and the increase in tetraploid nuclei in the growing livers of rats weighing from 40 up to 130 gm. can both be explained by the hypothesis that the tetraploid nuclei originate from the interphase diploid nuclei without involving mitosis. This hypothesis implies that mitosis is confined to the reproduction of diploid cells alone. 6. It is suggested that, in general, the synthesis of DNA does not necessarily result in the formation of visible mitotic chromosomes. 7. Mitotic time and generation time of diploid nuclei and the percentage of the tetraploidization from diploid nuclei are calculated and discussed.

Animals↗
PubMed1958

The two-wavelength method of microspectrophotometry. II. A set of tables to facilitate the calculations.

The calculations required for two-wavelength measurements are time consuming and laborious. In order to circumvent this limitation of the method, a set of tables which combined four operations into one has been designed and is reproduced within. The tables are based on Patau's formulae. The two transmission readings obtained according to the photometric method provide the coordinates which lead directly to a value for the relative absorbance. The product of this absorbance and the area of the photometric field gives the relative amount of chromophore in the field. The range of transmission values covered in the table corresponds to the effective range of the two-wavelength method.

Microspectrophotometry↗