Search PubMed⌕ Search

Biomedical subjects

S Clarke

Publications and source records attributed to S Clarke.

At least 397 records · Page 22Linked to original sources
PubMed1979

The effect of protein modification reagents on the chemotactic response in Salmonella typhimurium.

Several classes of reagents that covalently modify proteins have been shown to inhibit the ability of Salmonella typhimurium to reverse the direction of its flagellar rotation. Such reversal normally allows the bacterium to tumble and reorient its movement in a more favorable direction. These reagents include those that react with amino, guanidino, sulfhydryl, and disulfide groups on proteins. At high concentrations, most of these compounds also cause the paralysis of flagellar rotation. Tumbling in bacterial chemotaxis has been shown to be dependent on the methylation of a class of membrane proteins. The effects of these reagents in an in vitro methylation system have been studied. The results obtained suggest that most of these compounds are probably not acting on intact cells by inhibiting the activities of the cheR methyltransferase or the methyl-accepting proteins.

Aldehydes↗
PubMed1976

Protein asymmetry in the inner membrane of rat liver mitochondria.

At least three groups of polypeptides of the inner membrane of rat liver mitochondria have been shown to be exposed to the exterior surface by several techniques: lactoperoxidase-catalyzed iodination of mitochondria and inner membrane/matrix vesicles (mitoplasts), reaction of mitochondria and mitoplasts with the membrane-impermeable diazonium salt of sulfanilic acid, and controlled proteolysis of mitoplasts. These classes of proteins, separated by dodecyl sulfate gel electrophoresis, have polypeptide molecular weights of 73,000, 31,000, and 26,000. In addition, four other groups have been shown to be exposed to the exterior surface by at least one of these techniques: these components have polypeptide molecular weights of 130,000, 87,000, 16,000, and 10,500. A class of proteins, which makes up 50 to 60% of the total mitochondrial protein and which can be easily extracted from mitoplasts by freeze-thaw fractionation or other procedures designed to separate "matrix" protein from "membrane" protein, is shown not to be exposed to the outer surface of the inner membrane by these techniques. This class of proteins contains polypeptides of various molecular weights and includes the major 165,000 molecular weight polypeptide, identified with carbamyl phosphate synthetase.

Animals↗
PubMed1976

A major polypeptide component of rat liver mitochondria: carbamyl phosphate synthetase.

One of the major components of rat liver mitochondria detected by gel electrophoresis in sodium dodecyl sulfate is a 165,000 molecular weight polypeptide that makes up 15 to 20% of the total mitochondrial protein. This component appears to be a single molecular species. Evidence is presented here for the identification of this protein with the polypeptide chain of a urea cycle enzyme, carbamoylphosphate synthetase I (EC 2.7.2.5). The 165,000 molecular weight polypeptide was solubilized from mitochondria with Triton X-100 and purified to 90% homogeneity by DEAE-cellulose chromatography. This component co-migrated with carbamyl phosphate synthetase activity when mitochondrial proteins were separated by gel filtration or sucrose gradient centifugation. The identification of the 165,000 molecular weight polypeptide with this activity was also supported by the presence or absence of this protein in a variety of rat tissue mitochondria, in liver and kidney mitochondria from various ureotelic and nonureotelic species, and in fetal rat liver mitochondria.

Amino Acids↗
PubMed1975

The size and detergent binding of membrane proteins.

Sucrose density gradient centrifugation has been used to measure the binding of Triton X-100 above its critical micellar concentration to a variety of purified membrane and non-membrane proteins. In addition, binding studies were done on the three proteins below the critical micellar concentration of detergent to distinguish between the interaction of proteins with detergent monomers and detergent micelles. A procedure is described for the calculation of the molecular weight of these Triton X-100 protein complexes and measurements were made for opsin, plasma low density lipoprotein, the (Na-+ plus K-+)-dependent adenosine triphosphatase, the human red blood cell major sialoglycoprotein (PAS-1) and the human red blood cell minor glycoprotein (bandIII). These proteins behave as monomers or dimers in detergent and bind between 0.28 and 1.12 g of detergent per g of protein. A general method is also present for calculating the molecular size and shape of impure membrane proteins in detergent. Finally, Triton X-100 was shown to replace bound Na dodecyl-SO4 on the minor glycoprotein of the red blood cell.

Albumins↗