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Biomedical subjects

J Horwitz

Publications and source records attributed to J Horwitz.

At least 163 records · Page 9Linked to original sources
PubMed1981

Immunochemical studies on the major intrinsic polypeptides from human lens membrane.

Cell membranes from the human lens contain two major polypeptides with molecular weights near 26,000 and 22,000. These two species have been isolated in a highly purified state and purified by means of an antiserum against the 26,000 dalton membrane polypeptide from bovine lens. Immunochemical data are presented that establish a clear structural relationship between the two polypeptides and are consistent with the hypothesis that the 22,000 dalton species derived proteolytically from the 26,000 dalton species.

Adolescent↗
PubMed1981

Analysis of microdissected cataractous human lenses.

The potential of high-performance liquid chromatography (HPLC) as a technique for studying human cataractogenesis by analyzing minute quantities of lens proteins was demonstrated in a human retinitis pigmentosa (RP) lens. Individual human cortical cataractous lenses were microdissected. A well-defined opaque section was identified, the lens capsule was cut, and the section was removed. A nearby clear lens section was dissected out to serve as a control. Soluble crystallins from the cataractous and adjacent normal sections were subjected separately to gel filtration on a HPLC system. In the RP lens, the protein profiles obtained from an opaque polar-posterior subcapsular section and from nearby clear sections of the same lens were significantly different. The protein profile of an opaque area near the equator of the same RP lens was similar to nearby clear sections. These results show that different opaque zones in a single lens may have unique biochemical and biophysical properties.

Cataract↗
PubMed1980

The nucleotide sequence of two bovine lens phenylalanine tRNAs. Possible activation of a new phenylalanine tRNA gene during differentiation of lens cells.

Bovine lens fiber cells contain two major isoacceptors of phenylalanine tRNA, tRNA1Phe and tRNA2Phe whereas lens epithelial cells contain mainly tRNA2Phe (Ortwerth, B.J,, Yonuschot, G.R., Heidlege, J.F., Chu-Der, O.M.Y., Juarez, D., and Hedgcoth, C. (1975) Exp. Eye Res. 20, 417-426). Thus, the induction of a new species of tRNAPhe accompanies the differentiation of lens cells in vivo. These two species of tRNAPhe have been purified and their sequences have been analyzed. The results of the analyses show that the sequence of tRNA2Phe is identical with beef liver tRNAPhe while tRNA1Phe differs from tRNA2Phe by a guanosine to adenosine substitution at position 57. Therefore, the T psi CG sequence in the ribosylthymine loop of tRNA2Phe is replaced by T psi CA in tRNA1Phe, This observation demonstrates a case in which a change in sequence of tRNA isoacceptors accompanies cell development rather than changes in the level of post-transcriptional modification as noted in other systems (reviewed by Osterman L.A. (1979) Biochimie (Paris) 61, 323-342). The conversion of guanosine to adenosine in the ribosylthymine loop of lens tRNA1Phe suggests a possible activation of a new tRNAPhe gene during the differentiation of lens cells, although the possibility that this replacement may be catalyzed by a transglycosylase type enzyme has not been ruled out.

Animals↗
PubMed1980

The interaction of Cibacron Blue F3GA with troponin and its subunits.

Binding of troponin to Cibacron Blue F3GA-agarose column and its selective release from the gel in the presence of 0.5 M KCl provides the basis for a new purification method. The two-step procedure consists of isoelectric precipitation of tropomyosin and chromatography of the resultant crude troponin supernatant on Affi-Gel Blue column. Adsorption of troponin to the immobilized dye appears to occur through the troponin-T subunit. Troponin-I and troponin-C do not bind to the blue agarose column, whereas troponin-T binds to it very tightly. Binding of the dye to troponin-T prevents formation of troponin-T-troponin-C complex, but does not interfere with direct interaction of troponin-T with troponin-I. The activity of troponin in conferring calcium sensitivity on actomyosin ATPase is not affected by Cibacron Blue. Circular dichroism and difference absorption measurements of complexes of the blue dye with troponin and its subunits reveal the presence of a tight binding site on whole troponin and on troponin-T (KA greater than or equal to 10(6) M). The existence of weak binding sites for the dye on troponin and all of its subunits is deduced from difference absorption studies. Cibacron Blue appears to be a sensitive probe for subunit interactions in troponin.

Actins↗
PubMed1980

Pharmacokinetics of 5-fluorouracil administered orally, by rapid intravenous and by slow infusion.

Pharmacokinetic studies of 5-fluorouracil (5-FUra) were performed on 18 patients divided into three groups: seven patients were given 5-FUra i.v. by rapid injection; five patients received the drug p.o.; and six patients were treated by continuous i.v. infusion for 96 hr. The results showed rapid i.v. injection to be manifested by high early levels of drug achieved both in plasma and bone marrow with a rapid fall afterwards. Administration of 5-FUra p.o. gave rise to erratic plasma values due to greater variability in absorption, whereas 96-hr i.v. infusions showed constant levels of the drug in plasma and significantly (50- to 1000-fold) less 5-FUra in bone marrow. The main difference observed between rapid injection and slow infusion in the kinetics of the drug was the very high level of 5-FUra reached by rapid injection in plasma and bone marrow, which was of short duration (min) when compared to the low sustained levels observed during infusion. This route-dependent pharmacokinetic profile is consistent with the reported absence of myelosuppression in prolonged infusion and may be related to the resultant lower levels of 5-FUra achieved in bone marrow.

Adenocarcinoma↗
PubMed1979

The temperature and pH dependence of conformational transitions of the chromatin subunit.

Hydrodynamic, spectroscopic, and chemical crosslinking studies on monomer chromatin subnits are reported as a function of ionic strength, pH, and temperature. In earlier studies, two salt-dependent conformational transitions were described (Gordon et al., Proceedings of the National Academy of Science, 75, 660, 1978). Transition one occurred between 0.7 and 2.0 mM ionic strength and transition two occurred between 5.0 and 11.0 mM ionic strength. Crosslinking at 11 mM ionic strength with formaldehyde suppressed both transitions. In this communication we report that the second transition was characterized by changes in the circular dichroism spectra in the 260--320 nm region as well as by changes in the hydrodynamic properties. As the ionic strength was increased from 5.0 to 11.0 mM, [theta]282 decreased from 2000 TO 1500 DEG CM2/DMOLE AND [THETA]295 decreased from 0 to -400 deg cm2/dmole. Both transitions occurred in the pH range from pH 6.0 to 9.2. At pH 5.0, the two ionic strength-dependent transitions were no longer observed and the characteristic changes in the circular dichroism spectra were suppressed. The spectra of the monomer subunits at pH 5.0 showed only small changes with ionic strength and resembled the spectra of the subunits at 11 mM ionic strength above pH 6.0. In order to characterize the transitions in thermodynamic terms an ionic strength near the midpoint of each transition was selected. Then, changes in s20,w and D20,w were measured as a function of temperature. These data allow an estimation to be made of the enthalpies and entropies of the transitions.

Chromatin↗
PubMed1979

Interaction of troponin subunits. The interaction between the inhibitory and tropomyosin-binding subunits.

The interaction of troponin-I and troponin-T was demonstrated by circular dichroism and gel filtration. Troponin-I gives a negative circular dichroism band between 300 and 260 nm while troponin-T gives two weak positive bands, one at 290 nm and the other at 263 nm. When troponin-I and troponin-T were mixed, the complex produced a strong negative circular dichroism band with a maximum around 280 nm. This band was most intense with a molar ratio of troponin-T to troponin-I of 1:1. The intensity of the band was 2.4 times that expected from the separate components. The interaction was independent of salt concentration from 0.15 to 0.5 M KCl. Gel filtration on Sephacryl S-200 showed that a stable 1:1 complex was formed between troponin-T and troponin-I. When troponin-C was added to the complex of troponin-T.troponin-I; the reconstituted troponin had a circular dichroism spectrum identical to that of native troponin. The oxidation state of troponin-I was important in reconstituting troponin. Oxidized troponin-I produced less change in the near ultraviolet circular dichroism when added to troponin-T and the troponin-C than did reduced troponin-I. This showed the subunits were not assembled correctly with oxidized troponin-I. When the reconstituted complex was reduced, the circular dichroism was restored to that of native troponin. Troponin reconstituted with oxidized troponin-I did not confer calcium sensitivity on actomyosin ATPase; activity was restored by reducing the complex.

Circular Dichroism↗
PubMed1977

Partial dissociation and renaturation of embryonic chick delta-crystallin. Characterization by ultracentrifugation and circular dichroism.

1. delta-Crystallin from 15-day-old embryonic chick lenses was characterized by circular dichrosim (CD) spectroscopy. Examination by CD spectroscopy in the far ultraviolet (190-250 nm) demonstrated that the secondary structure of delta-crystallin has at least 75% alpha-helix; the delta-crystallin subunits dissociated in sodium dodecyl sulfate retain their alpha-helical content. This appreciable alpha-helical content of delta-crystallin contrasts with the absence of alpha-helix in other lens crystallins. 2. As judged by CD spectroscopy in the near ultraviolet (250-320 nm) the tertiary structure of embryonic delta-crystallin is not readily disrupted by environmental changes, such as NaCl, KSCN or the non-ionic detergent Emulphogene BC 720, and is stable to temperature fluctuation between 2 and 56 degrees C. 3. Experiments were directed towards deaggregation and renaturation of the four subunits of embryonic delta-crystallin by treatment with urea or guanidine hydrochloride. The native tertiary structure of delta-crystallin was lost above 4 M urea or 2 M guanidine hydrochloride, as judged by CD spectroscopy in the near ultraviolet. Ultracentrifugation at sedimentation equilibrium showed that in 4 M urea delta-crystallin dissociates into dimeric subunits, while in 2 M guanidine hydrochloride delta-crystallin exists as a mixture of dimeric and tetrameric subunits. Dialysis of delta-crystallin from 4 M urea resulted in reaggregation of the subunits into tetramers, about 50% of which showed native tertiary structure. Dialysis from 2 M guanidine hydrochloride also resulted in tetramer formation, and about 35% was recovered with native conformation. Removal of denaturant by dialysis produced no native teritary structure after treatment with 8 M urea, but about 15% native conformation after treatment with 6 M guanidine hydrochloride.

Animals↗