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Biomedical subjects

R M Dowben

Publications and source records attributed to R M Dowben.

At least 37 records · Page 2Linked to original sources
PubMed1977

Dielectric dispersion of actin.

The dielectric dispersion of G-actin was 7 X 10(6) Hz, and the low frequency reduced dielectric increment 0.99 +/- 0.15 ml/mg. The dielectric increment of F-actin in the range 10(5) to 10(8) Hz was very low, about 0.3.

Actins↗
PubMed1976

Isolation of membrane-bound renal enzymes that metabolize kinins and angiotensins.

Cortex of rat kidney was homogenized and fractions enriched in plasma membrane, endoplasmic reticulum or brush border were prepared by several techniques of differential centrifugation. The identity and homogeneity of the membrane fragments were investigated by assaying marker enzymes and by transmission and scanning electron microscopy. Kallikrein was present in both plasma-membrane- and endoplasmic-reticulum-enriched fractions isolated by two fractionation procedures. Kallikrein was highly concentrated in a plasma-membrane fraction but was absent from the brush-border membrane of proximal tubular cells. Cells of transplanted renal tumours of the rat, originating from the proximal tubule, had no kallikrein activity. Kininase activity, angiotensin I-converting enzyme (kininase II) and angiotensinase were found in a plasma-membrane-enriched fraction and especially in the fraction containing isolated brush border. It is suggested that after renal kallikrein is synthesized on endoplasmic reticulum, it is subsequently reoriented to a surface membrane for activation and release. Renal kallikrein may enter the tubular filtrate distal to the proximal tubules. The brush-border membrane of proximal tubule is the major site of inactivation of kinins and angiotensin II..

Adenosine Triphosphatases↗
PubMed1976

Cell-free translation of messenger RNA for a myeloma light chain prepared from synchronised plasmacytoma cells.

Crude preparations of biologically active mRNA, which code for a myeloma (MPC-11) light chain, were isolated by two successive sucrose gradient centrifugations of RNA extracted from membrane-bound ribosomes, mRNA thus obtained was separated into a poly(A)-rich and a poly(A)-poor fraction by oligo(dT)-cellulose chromatography. Both these fractions were able to direct the synthesis of light chains in reconstituted cell-free systems derived from heterologous cells (ascites tumor lysates) and homologous cells (MPC-11 cells grown in suspension culture). The identity of the products in vitro was confirmed by comparing their migration with that of light chains produced in vivo upon electrophoresis in sodium dodecylsulphate/polyacrylamide gels, and from the profiles of tryptic peptides obtained by chromatography on Aminex A-5 ion-exchange columns. Template activity of the poly(A)-rich light chain mRNA fraction showed very little variation during the cell cycle. The activity of the poly(A)-poor fraction on the other hand was maximal during the early S phase. It is concluded that maximal synthesis of immunoglobulins observed in vivo during the late G1 phase of the cell cycle is achieved by translational control mechanisms.

Aminoacylation↗
PubMed1976

Isolation of renal membranes that contain kallikrein, angiotensin I-converting enzyme (kininase II) and angiotensinase in the rat.

1. Fractions highly enriched in plasma membrane, endoplasmic reticulum or brush border were prepared from rat kidney cortex. Kallikrein was concentrated in the plasma membrane fraction, but not in the brush border fraction. Angiotensin I-converting enzyme (kininase II) and angiotensinase were localized in the brush border membrane. 2. It is suggested that kallikrein in the urine may originate from plasma membrane distal to the brush border of proximal tubules and the conversion of angiotensin I and the inactivation of bradykinin and angiotensin II may occur on the lumen membrane of the proximal tubular cells.

Animals↗
PubMed1976

Synthesis and secretion of light-chain immunoglobulin in two successive cycles of synchronized plasmacytoma cells.

Suspension-cultured mouse plasmacytoma cells (MPC-11) were accumulated in the late G1 phase by exposure to isoleucine-deficient medium for 20-24 h. The arrested culture was fed with complete medium enabling the cells to continue the cell cycle synchronously, undergo mitosis, and enter a second cycle of growth. This method of synchronization left the protein-synthesizing ability intact as judged by the polysome profile and the capacity of the cells to incorporate labeled amino acids into protein after the restoration of isoleucine. After incubation in isoleucine-deficient medium and the addition of isoleucine to the culture, cells entered the S phase after a short lag, as judged by [3H]thymidine incorporation into nucleic acid and by spectrophotometric measurement of nuclear DNA. The cells were in mitosis between 12 and 18 h as judged by the increase in cell count and analysis of cell populations on albumin gradients. Synthesis and secretion of light-chain immunoglobulin were maximal in the late G1/early S phase of the first cycle. During late S phase, G2 phase, and mitosis, both synthesis and secretion were observed to be at a low level; however, immediately after motosis the cells which then entered the G1 phase apparently commenced synthesis of light chain immunoglobulin straight away, although secretion of labeled material remained at a low level.

Cell Count↗
PubMed1975

Isolation of membrane-bound renal kallikrein and kininase.

Fractions highly enriched in plasma membrane, endoplasmic reticulum or brush border were prepared from homogenized rat kidney cortex. Kallikrein was concentrated in the plasma-membrane fraction, but not in the brush border of the proximal tubules. Kininase II or angiotensin I-converting enzyme was localized in the brush-border membrane. It is suggested that kallikrein in the urine may originate from the plasma membrane of the distal tubules and the conversion of angiotensin I and the inactivation of bradykinin may occur on the lumen membrane of the proximal tubular cells.

Animals↗
PubMed1973

Relatedness among contractile and membrane proteins: evidence for evolution from common ancestral genes.

A statistical method for quantifying the relatedness among proteins was used to perform 2926 paired comparisons of amino-acid composition among 77 contractile and membrane-associated proteins from diverse species and sources. Relatedness of amino-acid compositions correlates with homology of amino-acid sequence. A high degree of relatedness was detected among K(+)-dependent membrane ATPase of Streptococcus faecalis, coupling factors F(1) and CF(1) from mitochondria and chloroplasts, outer fiber protein of cilia, ciliary dynein, tubulin, various actins, and myosin subfragment S-1. Heavy meromyosin and tropomyosin were related to each other but not to the first group of proteins. Differences in the degree of methylation may account for some differences in physiological function. Because of their diverse sources, the high degree of relatedness among these proteins is more compatible with evolution from common ancestral genes than with convergent evolution. Squid axon filarin, molluscan paramyosin, and bacterial flagellins appear to be unrelated either to each other or to any of the other proteins studied. Existence of persistent homologies among so many diverse proteins implies conservation of genetic information during evolution by utilization of codons for preferred amino-acid sequences in various proteins.

Actins↗
PubMed1970

The molecular mechanism of force generation in striated muscle.

An electrostatic mechanism for force generation in muscle is proposed which does not require bond formation between thick and thin filaments nor movement of the cross bridges. The myosin heads, which project from the thick filaments and touch the thin filaments, possess a high negative surface charge density. Owing to their large dielectric increment, the thin filaments are polarized by the electric field generated by the myosin heads. The polarized thin filaments tend to move toward the center of the sarcomere. Myosin ATPase activity is increased in the overlap region to maintain the negative surface potential. Thus, ATP hydrolysis provides the energy for shortening. Calculations give estimated tensions generated by this model that are comparable to those observed experimentally for vertebrate striated muscle.

Adenosine Triphosphatases↗