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N T Yu

Publications and source records attributed to N T Yu.

At least 55 records · Page 3Linked to original sources
PubMed1985

Resonance Raman studies of CO and O2 binding to elephant myoglobin (distal His(E7)----Gln).

Carbon monoxide and dioxygen were employed as resonance Raman-visible ligands for probing the nature of the heme-binding site in elephant myoglobin, which has glutamine in the distal position (E7) instead of the usual histidine. The distal histidine (E7) residue has been thought to be responsible for weakening carbon monoxide binding to hemoproteins. It is of interest to see how the His(E7)----Gln replacement affects such parameters as nu(Fe-N epsilon), nu(Fe-CO), delta(Fe-C-O), nu(C-O), delta(Fe-O-O), and nu(O-O) vibrational frequencies and relative intensities. Elephant myoglobin has a CO affinity approximately 6 times higher than that for human/sperm whale myoglobin (Mb). If this enhanced affinity were solely due to the removal of some of the steric hindrance that normally tilts the CO off the heme axis, one would expect the nu(Fe-CO) frequency to decrease and the nu(C-O) frequency to increase relative to the corresponding values in sperm whale Mb. However, the opposite was found. In addition, strong enhancement of the Fe-C-O bending mode was observed. These results suggest that the Fe-C-O linkage remains distorted. In elephant Mb, new interactions resulting from the conformational change accompanying ligand binding may be responsible for the increased CO binding. Similar spectra were obtained for elephant and sperm whale oxymyoglobin. This suggests that the interactions of bound O2 are not markedly affected by the glutamine replacement.

Animals↗
PubMed1985

Disulfide bond formation in the eye lens.

The disposition and disposal of the -SH groups of the lens during aging and cataractogenesis have been investigated by laser Raman spectroscopy as a noninvasive microprobe in the intact living lens. In this procedure -SH and -S-S- give unique discrete Raman signals (at 2580 and 508 cm-1) that may be used to calculate relative concentrations in a very small volume of the lens. We present evidence showing an unexpected and remarkable difference with respect to these groups between the mouse lens and the lenses of guinea pig and man. The mouse lens nucleus exhibits a precipitous fall in the -SH concentration on aging from 1 to 6 months; concomitantly, there is a rise in -S-S- of comparable magnitude, indicating a direct conversion. The guinea pig lens, however, is quite different with respect to the age-dependent change in nuclear -S-S-: there is none between 6 months and 5 years. In the human lens -S-S- behaves exactly as in the guinea pig lens: the level is low and does not change with age between 9 and 65 years. With respect to nuclear -SH, these two latter species of lenses show some decrease with age but nothing like the approach to zero found in the aging mouse lens nucleus. These differences involving lenticular -SH and -S-S- appear to be correlated with the hard nucleus in the mouse lens and the softer nuclei of lenses in guinea pigs and humans. The relatively high level of -S-S- in the old but clear mouse lens does not support the idea that protein aggregation involving formation of intermolecular -S-S- bonds is necessarily an important cause of nuclear cataract. The small but significant age-related depression of -SH in guinea pig lens nuclei without any accumulation of -S-S- may be explained as a result of glutathione (GSH) oxidation and subsequent extrusion of glutathione disulfide (GSSG) by the lens. We propose that the oxidation of glutathione proceeds by reaction with protein disulfide groups to yield protein sulfhydryl (PSH) and a mixed disulfide of glutathione and protein; the mixed disulfide is capable of being reduced by glutathione reductase and NADPH, yielding the original PSH and GSSG, which is extruded from the lens. It remains to be determined if this mechanism is more active in guinea pig and human lenses than in the mouse lens.

Aging↗
PubMed1985

Fluorescence/Raman intensity ratio for monitoring the pathologic state of human lens.

The authors have put quantitation of human lens fluorescence on a rational basis by using the accompanying Raman signal from lens protein as a normalization factor. The intensity ratio, Fluorescence/Raman (F/R), may be used to compare lenses of different ages when the exciting wavelength is long enough to give a measurable Raman signal. In younger lenses excited at 457.9 or 514.5 nm, the F/R shows a log increase with age. Older lenses, above 60 years of age, excited at 647.1 nm give a steeply rising sigmoid curve. In developing this procedure, the authors found that for each lens there is a characteristic wavelength that is called the critical wavelength (lambda critical). At wavelengths longer than lambda critical the Raman signal appears in the absence of a broad fluorescence peak; at shorter wavelengths the fluorescence intensity increases enough to overwhelm the Raman signal. For normal lenses, clear and not heavily pigmented, the lambda critical is age dependent, giving a curve that is a flattened sigmoid approximating a straight line.

Adolescent↗
PubMed1984

Assignment of the Fe-N epsilon (His) stretching mode in the resonance Raman spectra of a monomeric insect cyanomethaemoglobin.

Resonance Raman (RR) spectra of the monomeric cyanomethaemoglobin CTT III from insect larvae of Chironomus thummi thummi are shown for the range of 200-550 cm-1. By iron and cyanide isotope exchange a line varying between 307 cm-1 for 57Fe-13C15N and 311 cm-1 for 54Fe-12C14N, has been assigned to the Fe-N epsilon stretching mode of this haem complex. The substitution of 54Fe for 57Fe has no effect on the Fe-C = N bending mode whereas it affects the Fe-CN stretching mode.

Animals↗
PubMed1984

Iron-carbon bond lengths in carbonmonoxy and cyanomet complexes of the monomeric hemoglobin III from Chironomus thummi thummi: a critical comparison between resonance Raman and x-ray diffraction studies.

Soret-excited resonance Raman spectroscopy yields direct information regarding the iron-carbon bonding interactions in the cyanomet and carbonmonoxy complexes of hemoglobin III from Chironomus thummi thummi (CTT III) in solution. By isotope exchange in cyanide (13CN-, C15N-, and 13C15N-) and carbon monoxide (13CO, C18O, and 13C18O), we have assigned the Fe(III)-CN- stretching at 453 cm-1, the Fe(III)-C-N- bending at 412 cm-1, the Fe(II)-CO stretching at 500 cm-1, the Fe(II)-C-O bending at 574 cm-1, and the C-O stretching at 1960 cm-1. The resonance Raman data, in conjunction with those obtained from heme model complexes with well-known Fe-C bond distances, strongly suggest that the Fe(III)-CN- bond (approximately 1.91 A) is longer (hence weaker) than the Fe(II)-CO bond (approximately 1.80 A). This result disagrees with those of x-ray crystallographic studies [Steigemann, W. & Weber, E. (1979) J. Mol. Biol. 127, 309-338] in which the Fe-C bond lengths were reported as 2.2 A in cyanomet and 2.4 A in carbonmonoxy CTT III. Based on Badger's rule and normal mode calculations, the x-ray data would lead to the prediction of 279 cm-1 for the Fe(II)-CO stretching frequency in CTT III . CO, which was not observed. On the other hand, we estimate the Fe-CO bond as approximately equal to 1.82 A, which is very similar to the 1.80-A value in human Hb . CO crystals. Furthermore, we have used isotope shift data to estimate the Fe-C-O angle as 169 +/- 5 degrees, somewhat larger than the 161 degrees value found by Steigemann and Weber. We therefore conclude that there must be errors in the x-ray crystallographic refinement for the ligand geometry in carbonmonoxy and cyanomet CTT III.

Animals↗
PubMed1984

Fluorophors and chromophors from rat lens crystallins in UV with hydroxykynurenine.

Isolated alpha-, beta-, and gamma-crystallins from young rat lenses were incubated in solution for 16 hr with 3-hydroxykynurenine under ultraviolet (366 nm) light. Controls included: incubation without light, without kynurenine, and with 2-mercaptoethanol. These procedures generated several chromophors (with absorption maxima or shoulders at 340, 370, and 470 nm) and fluorophors (with excitation/emission at 407/515, 458/550, 515/555, 647/664, and 647/740 nm). The formation of these pigments was inhibited by 2-mercaptoethanol. The findings are discussed in relation to the chromophors and fluorophors found in aged and brunescent human lenses.

Animals↗
PubMed1983

Resonance Raman studies of carbon monoxide binding to iron "picket fence" porphyrin with unhindered and hindered axial bases. An inverse relationship between binding affinity and the strength of iron-carbon bond.

The stretching frequency of the iron-carbon bond, v(Fe-CO), is a direct measure of the iron-carbon bond strength when there is no change in the Fe-C-O geometry. Here we report resonance Raman detection of v(Fe-CO) frequencies in the CO complexes of iron (II) alpha, alpha, alpha, alpha-mesotetrakis(o-pivalamidophenyl)porphyrin, FeII(TpivPP), with trans ligands of varying strength: N-methylimidazole (N-MeIm), 1,2-dimethylimidazole (1,2-Me2Im), pyridine (py), and tetrahydrofuran (THF). It was found that the weaker the iron-trans ligand bond, the stronger the iron-carbon bond. Comparisons of sterically hindered (1,2-Me2Im) and unhindered (N-MeIm) bases are of particular interest because of their implication in the phenomenon of hemoglobin cooperativity and the mechanisms of protein control of heme reactivity. While the CO binding affinity of FeII(TpivPP)(1,2-MeIm) is approximately 400 times lower than that of FeII(TpivPP)(N-MeIm), the v(Fe-CO) frequency for the former (at 496 cm-1) is higher than that for the latter (at 489 cm-1). This example shows that the CO binding affinity cannot be directly correlated with the strength of the iron-carbon bond. Comparison of the CO binding to FeII(TpivPP)(THF) and FeII(TpivPP)(N-MeIm) reveals a similar relationship; the v(Fe-CO) frequency (at 527 cm-1) in FeII(TpivPP)(THF)(CO) is 38 cm-1 higher than that in FeII(TpivPP)(N-MeIm)(CO), but the CO binding affinity is lower for the THF complex.

Carbon Monoxide↗
PubMed1983

Resonance Raman detection of Fe-CO stretching and Fe-C-O bending vibrations in sterically hindered carbonmonoxy "strapped hemes". A structural probe of Fe-C-O distortion.

We report resonance Raman studies of the Fe-C-O distortion in sterically hindered heme-CO complexes. The steric hindrance is provided by a hydrocarbon chain strapped across one face of the heme. Increasing the steric hindrance (by decreasing the chain length), which reduces the CO binding affinity, is found to increase the Fe-CO stretching frequencies: heme 5 (unstrapped), 495 cm-1; FeSP-15, 509 cm-1; FeSP-14, 512 cm-1; FeSP-13, 514 cm-1. This is interpreted in terms of a decrease in the CO effective mass and increased interactions between the C atom of CO and the N atom(s) of the pyrrole ring(s). Resonance Raman enhancement of the Fe-C-O bending mode upon Soret excitation may be correlated with the overlap between the porphyrin (pi*) and CO (pi*) orbitals when the CO ligand is tilted. Its intensity relative to that of the Fe-CO stretching mode increases with increasing steric hindrance in these "strapped hemes". In addition, we have estimated the Fe-C-O angles from isotope data in various heme-CO complexes. It is inferred that the angles are 167 +/- 5 degrees (FeSP-15) and 175 +/- 5 degrees (FeSP-14, FeSP-13, Mb X CO, and Hb X CO).

Carbon Monoxide↗
PubMed1983

Resonance Raman studies of Co-O2 and O-O stretching vibrations in oxy-cobalt hemes.

Strong evidence suggests that the stretching vibration of the bound oxygen can be perturbed by an accidentally degenerate porphyrin ring mode, resulting in two split frequencies. In the Co(II)(TpivPP) (pyridine) (18)O(2) complex, we demonstrate that the nu((18)O-(18)O) mode, after being shifted from its nu((16)O-(16)O) value at 1,156 cm(-1), undergoes a resonance interaction with the 1,080 cm(-1) porphyrin mode, giving rise to two lines at 1,067 and 1,089 cm(-1). In the O(2) complex of Co(II) mesoporphyrin IX-substituted sperm whale myoglobin, we observed a dramatic intensity increase at 1,132 cm(-1) upon (16)O(2) --> (18)O(2) substitution, which is due to the reappearance of the 1,132-cm(-1) porphyrin mode after the removal of resonance conditions. A decrease in O(2) binding affinity, caused by the proximal base tension, corresponds to an increase in the Co-O(2) stretching frequency. The nu(Co-O(2)) at 527 cm(-1) for the low affinity Co(II)(TpivPP)(1,2-Me(2)Im) O(2) complex is 11 cm(-1) higher than the 516-cm(-1) value for the high affinity complex (with N-MeIm replacing 1,2-Me(2)Im). However, in the corresponding iron complexes the reverse behavior is observed, i.e., the nu(Fe-O(2)) decreases for the (1,2-Me(2)Im) complex. There is a 24-cm(-1) difference in the Co-O(2) stretching frequencies between Co(II)(TpivPP)(N-MeIm)O(2) (at 516 cm(-1)) and oxy meso CoMb (at 540 cm(-1)), suggesting a protein induced distortion of the Co-O-O linkage. However, the values for nu(Fe-O(2)) are nearly identical between Fe(II)(TpivPP)(N-MeIm)O(2) (at 571 cm(-1)) and oxy Mb (at 573 cm(-1)), indicating that O(2) binds to myoglobin in the same manner as in the sterically unhindered "picket fence" complex. Evidence is presented that suggests the presence of two dioxygen stretching frequencies due to two different conformers in each of the N-MeIm and 1,2-Me(2)Im complex of oxy Co(II)(TpivPP).

Animals↗
PubMed1983

Resonance Raman studies of nitric oxide binding to ferric and ferrous hemoproteins: detection of Fe(III)--NO stretching, Fe(III)--N--O bending, and Fe(II)--N--O bending vibrations.

The nature of bonding interactions between Fe(III) and NO in the ferric nitrosyl complexes of myoglobin (Mb), hemoglobin A (HbA), and horseradish peroxidase (HRP) is investigated by Soret-excited resonance Raman spectroscopy. On the basis of 15NO and N18O isotope shifts, we clearly identified the Fe(III)--NO bond stretching frequencies at 595 cm-1 (ferric Mb X NO), 594 cm-1 (ferric HbA X NO), and 604 cm-1 (ferric HRP X NO). The Fe(III)--N--O bending vibrations are located at 573 cm-1 (ferric Mb X NO) and 574 cm-1 (ferric HRP X NO), which are very similar to the Fe(II)--C--O bending modes at 578 cm-1 in Mb X CO and HbA X CO. However, the Fe(III)--NO and Fe(II)--CO stretching frequencies differ by approximately equal to 90 cm-1, indicating a much stronger iron-axial ligand bond for the [Fe(III) + NO] system, which is isoelectronic with the [Fe(II) + CO] system and, hence, presumably also has a linear Fe(III)--N--O linkage (in the absence of distal steric effect). The unusually strong Fe(III)--NO bond may be attributed to the pi bonding involving the unpaired electron in the pi (NO) orbital. The N18O isotope shift data indicate that the widely accepted assignment of the Fe(II)--NO stretching vibration at approximately equal to 554 cm-1 in ferrous nitrosyl Mb/HbA is incorrect; instead, we assign it to the Fe(II)--N--O bending mode. The validity of the assignment of Fe(II)--O2 stretch at 567 cm-1 in oxy-HbA by Brunner [Brunner, H. (1974) Naturwissenschaften 61, 129-130] is now in doubt. Literature data are presented to suggest that it is the Fe(II)--O--O bending vibration.

Animals↗
PubMed1983

Metabolic production of a blue-green fluorophor in lenses of dark-adapted mice and its increase with age.

A blue-green fluorophor (496 nm emission/406.7 nm excitation) occurs in the mouse lens; its increase with age is more pronounced in the nucleus than in the cortex. The level of fluorophor and its rate of production are the same for animals reared in the dark as for animals reared in the light. Thus, the fluorophor is not generated by a photochemical reaction but is a purely metabolic product.

Aging↗
PubMed1982

Resonance Raman investigation of nitric oxide bonding in nitrosylhemoglobin A and -myoglobin: detection of bound N-O stretching and Fe-NO stretching vibrations from the hexacoordinated NO-heme complex.

With excitation at 406.7 nm, we have observed the resonance Raman enhancement of the bound v(N-O) stretch at approximately 1623 cm-1 in nitrosylhemoglobin A and nitrosylmyoglobin, indicating the existence of a charge-transfer transition underlying the strong Soret band. The v(Fe-NO) stretch at 551 cm-1 has also been detected in the Soret as well as in the Q-band region, a phenomenon similar to the v(Fe-O2) and v(Fe-CO) stretches in oxy and carbon monoxy hemoproteins. It appears that these iron-ligand vibrations ay be resonance enhanced via porphyrin pi leads to pi transitions. Upon addition of inositol hexaphosphate at pH 6.0, the v(Fe-NO) stretch at 551 cm-1 and a low-frequency mode at 301 cm-1 exhibit an intensity decrease by approximately one-half. Contrary to the work of Stong et al. [Stong, J. D., Burke, J. M., Daly, P., Wright. P., & Spiro, T. G. (1980) J. Am. Chem. Soc. 102, 5815], who employed an excitation wavelength at 454.5 nm, we observed no intensity increase at 592 cm-1 attributable to the v(Fe-NO) stretch from the pentacoordinated NO-heme complex in the alpha subunits.

Animals↗
PubMed1981

Temperature dependence of resonance Raman spectra of metmyoglobin and methemoglobin azide. Detection of resonance-enhanced bound azide vibrations and iron-azide stretch.

Resonance Raman spectroscopy has been employed to study the thermal spin equilibria in metmyoglobin azide [Fe(III)Mb-N3] and methemoglobin azide [Fe(III)-Hb-N3]. The effect of temperature on Raman intensities permits us to assign lines to either high- or low-spin species. With excitation at 647.1 nm the intensity of an 15N3 isotope-sensitive mode at approximately 411 cm-1 was found to increase with decreasing temperature, indicating that its origin may not be the high-spin charge-transfer band at approximately 640 nm as suggested by Asher & Schuster [Asher, S. A. & Schuster, T. M. (1979) Biochemistry 18, 5377]. Instead, it may be enhanced via the weaker low-spin z-polarized charge-transfer band at approximately 650 nm which was identified by Eaton & Hochstrasser [Eaton, W. A., & Hochstrasser, R. M. (1968) J. Chem. Phys. 49, 985]. Our normal coordinate analysis on the model azide-Fe-imidazole and the polarized nature of the line allow us to establish that the approximate 411-cm-1 mode in Fe(III)Mb-N3 and Fe(III)Hb-N3 is assignable to the Fe-N3 stretch of low-spin species. Furthermore, we assign the out of plane azide mode (low spin) to the depolarized line at 573 cm-1 (15N3 isotope sensitive), which was previously assigned as the Fe-N3 stretch by Desbois et al. [Desbois, A., Lutz, M., & Banerjee, R. (1979) Biochemistry 18, 1510]. No internal vibrations of bound azide excitation at 406.7 nm, we have observed the enhancement of the antisymmetric azide stretch (both high and low spin), out of plane bending (low spin), and Fe-N3 stretch (low spin), indicating the existence of at least two charge-transfer transitions underlying the strong Soret band. The following four types of charge transfer are discussed in the light of our present resonance Raman data: (1) porphyrin (pi) leads to high-spin Fe (d pi), (2) azide (n) leads to low-spin iron (dz2), (3) azide (pi) leads to low-spin iron (dz2), and (4) azide (pi) leads to porphyrin (pi) (high spin).

Animals↗
PubMed1981

Resonance Raman investigation of dioxygen bonding in oxycobaltmyoglobin and oxycobalthemoglobin: structural implication of splittings of the bound O--O stretching vibration.

Splittings related to the stretching vibration of bound dioxygen in hemoproteins have been detected by resonance Raman spectroscopy. With excitation at 406.7 nm we observe three isotope-sensitive lines in oxycobaltmyoglobin (oxyCoMb) [or in oxycobalthemoglobin A (oxyCoHbA)] at 1103 (1107), 1137 (1137), and 1153 (1152) cm-1, of which the most intense one appears at 1137 cm-1. The first two frequencies arise from resonance interaction between a v(O--O) mode at approximately 1122 cm-1 and an accidentally degenerate porphyrin ring mode at 1123 (1121) cm-1, whereas the third one represents an "unperturbed" v(O--O) vibration from a different species. These two v(O--O) modes at approximately 1122 and approximately 1153 cm-1 shift to approximately 1066 and approximately 1096 cm-1, respectively, upon 16O2 leads to 18O2 substitution. The same resonance interaction may also occur in oxyFeMb (probably also in oxyFeHb(a), because it exhibits an intensity increase at 1125 cm-1 upon 16O2 leads to 18O2 substitution, although the v(O--O) vibrations have not been observed directly. Concomitant enhancement is observed in the v(Co--O) vibration at 539 (537( cm-1, which is considerably lower than the v(Fe--O) frequency at approximately 570 cm-1 in oxyFeMb and oxyFeHbA. The Co--O bond is longer and weaker than the Fe--O bond. Enhancement of both v(O--O) and v(Co--O) indicates the existence of a charge-transfer transition underlying the Soret band, which may be assigned as pi*(pi g*O2/xz) leads to sigma*(dz2Co/pi g*). The presence of two v(O--O) vibrations (at approximately 1122 and approximately 1152 cm-1) but only one v(Co--O) mode at approximately 538 cm-1) means that the two species in oxyCoMB or oxyCoHbA have the same Co--O bond lengths but different O--O bond lengths. The bound dioxygen in a bent end-on configuration may have two allowed orientations, which differ in the extent of sp2(N epsilon) leads to pi*(O2) donation from distal histidine.

Animals↗
PubMed1980

Resonance Raman spectra of manganese myoglobin and its azide complex. Assignment of a new charge-transfer band to azide (pi) to porphyrin (pi) transition.

The enhancement of bound azide vibrations at 650 [depolarized (dp), bending] and 2039 cm-1 (dp, antisymmetric stretch) upon excitation at approximately 400-460 nm indicates the existence of a new charge-transfer transition in manganese(III) myoglobin-azide complex. The assignments of these two vibrational modes are based on the agreement of their 15N3 isotope shifts (22 and 70 cm-1) with the calculated values (22 and 69 cm-1), the depolarized nature, and their close proximity to the corresponding vibrations in ionized azide. The Mn-(III)-N3 stretch has not been observed in the present study although the Fe(III)-N3 stretch at 413 cm-1 (polarized) was reported [Asher, S. A., Vickery, L. E., Schuster, T. M., & Sauer, K. (1977) Biochemistry 16, 5849]. The RR spectra of MnIIIMb-azide between 150 and 300 cm-1 differ dramatically from those of FeIIIMb-azide exicted in the 640-nm charge-transfer band or near the Soret band. There are lines at 170 and 282 cm-1 (both polarized) in the MnIIIMb-azide spectra which exhibit extremely large resonance enhancements and are unshifted by 15N3 isotope substitution. These two lines, having no analogue in other heme protein spectra, may be tentatively assigned to the out-of-plane porphyrin ring vibrations, with the latter involving significant Mn(III)-N(pyrrole) stretch. The enhancement of non totally symmetric azide modes suggests that the charge-transfer state may be mixed with other excited electronic states (possibly band Va or band VI) via Herzberg-Teller vibronic couplings. The lack of enhancement of the Mn(III)-N3 stretch leads to our present assignment of azide (pi) to porphyrin (pi) charge-transfer transition rather than azide (pi) to metal (dz2) or azide (n) to metal (dz2).

Azides↗
PubMed1979

A Raman spectroscopic study of the interaction of divalent metal ions with adenine moiety of adenosine 5'-triphosphate.

Raman spectra of ATP at various pH values are affected by addition of equimolar solution of divalent metal ions such as Ca2+, Mg2+, Co2+, Cu2+, and Hg2+. The changes in frequency and intensity have been used to construct models describing the nature of metal-adenine and metal-triphosphate interactions under different conditions. The metal ions are found to co-ordinate the triphosphate group in the entire pH range studies (pH to 12). Calcium (II) and magnesium (II) interact strongly with the phosphate moiety at neutral pH, although a weak interaction with the ring occur at low pH values. Around neutrality, several Raman spectral changes are observed to implicate the interaction of cobalt (II) ion with the five-membered ring of the adenine. The changes in Raman frequency are too small to suggest a direct Co(II)-N7 binding. At least six different Cu(II)-ATP species are identified between pH 3 and 12. At pH approximately 7.0 Raman data are explained better by Cu(II) interacting with N7 simultaneously with the amino group of the adenine ring. However, a Cu(II) binding to N3 at pH 10 to 11 is indicated by the enhancement of the 760 and 1360 cm-1 vibrations. At neutral pH, mercury (II) ion shows a direct coordination at N1 while at low pH with N1 blocked by protonation, mercury (II) does not interact with the adenine moiety.

Adenine↗