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Biomedical subjects

B M Fung

Publications and source records attributed to B M Fung.

At least 37 records · Page 2Linked to original sources
PubMed1983

The effect of ATP concentration on the rate of actin polymerization.

It was found that the rate of polymerization of G-actin increased with the decrease of ATP concentration. When excess ATP was replaced by chloride through anion-exchange treatment, the extent of actin polymerization did not change provided that the ionic strength was raised immediately after the treatment. In the meantime, the rate of actin polymerization was greatly enhanced after the removal of excess ATP. The rate enhancement was much less when both excess Ca2+ and excess ATP were removed. G-actin with excess ATP replaced by chloride had larger light scattering and showed a "catalytic" effect on the polymerization of normal G-actin. The inhibition of actin polymerization by cytochalasin B in 100 mM KCl was much more obvious for G-actin with excess ATP removed than for normal G-actin. It is suggested that the reduction of excess ATP concentration in a G-actin solution increases the binding of weak-affinity Ca2+ and promotes the formation of oligomeric actin (actin nuclei).

Actins↗
PubMed1981

Nuclear magnetic resonance transverse relaxation in muscle water.

The origin of the nonexponentiality of proton spin echoes of skeletal muscle has been carefully examined. It is shown that the slowly decaying part of the proton spin echoes is not due to extracellular water. First, for muscle from mice with in vivo deuteration, the deuteron spin echoes were also nonexponential, but the slowly decaying part had a larger weighing factor. Second, for glycerinated muscle in which cell membranes were disrupted, the proton spin echoes were similar to those in intact muscle. Third, the nonexponentiality of the proton spin echoes in intact muscle increased when postmortem rigor set in. Finally, when the lifetimes of extracellular water and intracellular water were taken into account in the exchange, it was found that the two types of water would not give two resolvable exponentials with the observed decay constants. It is suggested that the unusually short T2's and the nonexponential character of the spin echoes of proton and deuteron in muscle water are mainly due to hydrogen exchange between water and functional groups in the protein filaments. These groups have large dipolar or quadrupolar splittings, and undergo hydrogen exchange with water at intermediate rates. The exchange processes and their effects on the spin echoes are pH-dependent. The dependence of transverse relaxation of pH was observed in glycerinated rabbit psoas muscle fibers.

Animals↗
PubMed1980

Modification of cell membrane lipids in Micrococcus lysodeikticus induced by pantoyl lactone.

Growth of Microccoccus lysodeikticus in the presence of pantoyl lactone brings about both qualitative and quantitative changes in cell membrane lipids. Significant amounts of the two major phospholipids (phosphatidylglycerol and diphosphatidylglycerol) are converted to lyso forms; the largest conversion occurs in the phosphatidylglycerol. In addition, amounts of several phospholipid fatty acids are changed. Physical alteration of the call membrane can be demonstrated using differential scanning calorimetry. Although growth and transport are significantly inhibited when pantoyl lactone is present, cells possessing altered call membrane phospholipds and phospholipid fatty acids, brought about by growth in the presence of pantoyl lactone, transport D-alanine, L-glutamic and L-aspartic acid normally when washed free of the pantoyl lactone.

4-Butyrolactone↗
PubMed1980

Varied magnetic field, multiple-pulse, and magic-angle spinning proton nuclear magnetic resonance study of muscle water.

The nuclear magnetic resonance linewidth of 1H in water of frog muscle was studied as a function of magnetic field strength and angle of orientation. The results suggest that the observed spectra are dominated by demagnetization field anisotropy and dispersion, but a small static dipolar interaction of the order of a few hertz man be present. Data from line-narrowing, multiple-pulse experiments also indicate the presence of a small dipolar broadening.

Animals↗
PubMed1979

Study of spin-lattice and spin-spin relaxation times of 1H, 2H, and 17O in muscular water.

Spin-lattice (T1) and spin-spin (T2) relaxation times of proton, deuteron, and oxygen-17 in muscle water have been measured at 9.21 MHz in the temperature range of 0 degree--40 degrees C. The values of the apparent activation energy for the three nuclei are (in kJ . mol-1) 9.1, 19, and 18 for 1/T1, and -1.3, 4.2, and 14 for 1/T2, respectively. The relatively small values for T2 for 1H and 2H and their low apparent activation energies are attributed to hydrogen exchange between water and proteins; this exchange does not affect the 17O relaxation. Quantitative calculations on deuteron T1 and oxygen-17 T1 and T2 have been made. The effect of surface-induced anisotropy on a minor fraction of water molecules is considered in some detail, and a new expression for its spectral density similar to that of liquid crystalline systems is applied in the calculation. It is suggested that water on the surfaces of macromolecules has a rotational correlation time of tau c approximately 1 x 10(-9) S, with a time constant of tau x approximately 3 x 10(-7) S, which is characteristic of the relaxation of the local structure.

Animals↗
PubMed1977

Correlation of relaxation time with water content in muscle and brain tissues.

Proton T1 of water in muscle and brain tissues was studied as a function of water content at 25 degrees C and 5, 30, and 100 MHz. Muscle samples were bathed in modified Krebs solutions that have the same ionic strength but different osmolarity in order to change the water content. At all three frequencies their 1/T1 extrapolated to the same value of 0.6 S-1 for zero dry weight, indicating that T1 for the majority of water molecules in normal muscle and brain is frequency-independent. Dehydrated muscle, homogenized brain tissue suspended in modified Krebs solution and dehydrated brain tissue provide samples with wide ranges of water content. Their T1 values at all three frequencies can be well accounted for by a simple equation derived from the two-state model.

Animals↗
PubMed1977

Carbon-13 and proton magnetic resonance of mouse muscle.

It is shown that roughly 4 mmol carbon atoms/g mouse muscle can give rise to a "high resolution" 13C NMR spectrum. From the 13C spectrum, it is estimated that the protons from mobile organic molecules or molecular segments amount to 6-8%of total nonrigid protons (organic plus water) in muscle. Their spin-spin relaxation times (T2) are of the order of 0.4-2 ms. At 37 degrees C, the proton spin-echo decay of mouse muscle changes rapidly with time after death, while that of mouse brain does not.

Animals↗
PubMed1977

Proton and deuteron relaxation of muscle water over wide ranges of resonance frequencies.

The spin-lattice relaxation time (T1) of water protons in mouse muscle was studied from 10(4) to 10(8) Hz at several temperatures, and the deuteron T1 of muscle water was studied from 2.0 X 10(3) to 1.54 X 10(7) Hz at several temperatures. Proton T1's of muscle and brain water with different D2O contents were measured at 25 degrees C and 35 MHz. From the results of variable frequency and temperature measurements and the data of isotope substitution, it is concluded that the major relaxation mechanism for the protons in muscle water is the intermolecular dipolar interaction between the protons of the macromolecules and the protons of the water molecules in the hydration layer. It is also suggested that the relaxation of deuterons can be accounted for a very small fraction of water molecules directly hydrogen-bonded to the macromolecules.

Animals↗
PubMed1976

The interaction between water and the polar head in inverted phosphatidylcholine micelles. A 2H and 31P relaxation study.

2H and 31P spin-lattice relaxation times (T1) were studied for inverted egg phosphatidylcholine micelles in CCl4 as functions of 2H2O concentration. When the 2h2O/phosphatidylcholine mole ratio changed from 1.0 to 18.0, T1 of 31P increased by about 2.6 fold, whereas T1 of 2H increased by about 50 fold. A quantitative analysis of the deuterium T1 data showed that there is only one water molecule tightly bound to the polar head, and it is in rapid exchange with the rest of the water molecules. The activation energy for the deuterium T1 was 7.1 +/- 0.8 kcal/mol(30 +/- 3 kJ/mol), and was independent of the 2H2O concentration.

Calorimetry↗
PubMed1976

The nature of bile salt micelles as studied by deuterium NMR.

Deuterium NMR of 3alpha,12alpha-dihydroxy-7,7dideutero-5beta-cholanic acid was studied. Molcular sizes obtained from deuterium spin-lattice relaxation time (T1) data of 3alpha,12alpha-dihydroxy-7,7-dideutero-5beta-cholanoic acid in methanol and in water are in accordance with monometic and tetrameric structures in the two media, respectively. The deuterium T1 and intensity of 3alpha,12alpha-dihydroxy-7,7-dideutero-5beta-cholanoic acid in aqueous solution at pH 8.0--8.8 were studied as functions of NcC1 and lecithin concentrations. The results indicated that tetramers are in equilibrium with larger aggregates when secondary micelles are formed in the precense of NaC1, and that 3alpha,12alpha-dihydroxy-7,7-dideutero-5beta-cholanoic acid forms mixed micelles with lecithin with a molecular ratio of 2 : 3.

Colloids↗
PubMed1975

Orientation of water in striated frog muscle.

Proton and deuterium nuclear magnetic resonance spectra of striated frog gastrocnemius muscle exhibit angular dependence, indicating partial orientation of water in the muscle. Nonzero static dipolar and quadrupolar interactions resulting from the anisotropic motion of the water molecules modulate the spin echo decays, contributing to their nonxponential behavior.

Animals↗
PubMed1975

The state of water in biological systems as studied by proton and deuterium relaxation.

Careful experiments on the measurement of the intensity of the deuterium NMR signal for 2-H2 O in muscle and in its distillate were performed, and they showed that all 2-H2 O muscle is "NMR visible". The spin-lattice relaxation time (T1) of the water protons in the muscle and liver of mice and in egg white has been studied at six frequencies ranging from 4.5 to 6.0 MHz over the temperature range of +37 to --70 degrees C. T1 values of deuterons in 2H2 O of gastrocnemius muscle and liver of mice have been measured at three frequencies (4.5, 9.21 and 15.35 MHz) over the temperature range of +37 to --20 degrees C. Calculations on T1 for both proton and deuteron have been made and compared with the experimental data. It is suggested that the reduction of the T1 values compared to pure water and the frequency dependence of T1 are due to water molecules in the hydration layer of the macromolecules, and that the bulk of water molecules in the biological tissues and egg white undergoes relaxation like ordinary liquid water.

Animals↗
PubMed1975

Water in normal muscle and muscle with a tumor.

The total water content, the amount of non-freezable water, and the Na-+ and K-+ contents in the gastrocnemius muscle of albino mice with and without a solid tumor were determined. The spin-lattice relaxation time (T1) for the water protons in the two kinds of muscle were measured at six resonance frequencies ranging from 4.5 to 60 MHz over the temperature range +37 to minus 65 degrees C. Quantitatively calculated T1 values are given. The difference in T1 for the two types of muscle at temperatures above minus 5 degrees C is attributed to the difference in the distribution ratio of water between hydration and free states, and bears no direct relation to the concentration of Na-+.

Animals↗