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Biomedical subjects

M Kahn

Publications and source records attributed to M Kahn.

At least 127 records · Page 7Linked to original sources
PubMed1980

Genetic analysis of bacteriophage P4 using P4-plasmid ColE1 hybrids.

A set of plasmids that contain fragments of the bacteriophage P4 genome has been constructed by deleting portions of a P4-ColE1 hybrid. A P4 genetic map has been established and related to the physical map by examining the ability of these plasmids to rescue various P4 mutations. The P4 virl mutation and P4 genes involved in DNA replication (alpha), activation of P2 helper genes (delta and epsilon), polarity suppression (psu) and head size determination (sid) have been mapped, as has the region responsible for synthesis of a nonessential P4 protein. One of the deleted plasmids contains only 5900 base pairs (52%) of P4 but will form plaques if additional DNA is added to increase its total size to near that of P4. This plasmid is also unique in that it will not form stable associations with P2 lysogens of E. coli which are recA+. P4 alpha mutants can be suppressed as a result of replication under control of the ColE1 part of the hybrid.

Chromosome Mapping↗
PubMed1980

Adjunctive arteriovenous fistula with tibial and peroneal reconstruction for limb salvage.

Arteriovenous fistulas were constructed as an adjunct to femoral peroneal and tibial bypasses in 13 patients threatened by imminent limb amputation. Previous attempts at conventional vascular reconstructive procedures had failed in nine patients. Deficient or absent pedal arches were noted in all patients, as were poor quality or small crural arteries. Graft patency was achieved in 11 cases and limb salvage in 10. There was no mortality. A steal phenomenon occurred in one patient and was successfully treated by secondary popliteal vein ligation. These preliminary results clearly indicate that an adjunctive arteriovenous fistula can maintain patency in a femoral tibial or peroneal bypass graft while preserving flow into the markedly diseased distal circulation.

Aged↗
PubMed1980

Demonstration of an antibody to tubular epithelium in glomerulonephritis associated with obstructive uropathy.

It has been postulated that in some patients with obstructive and reflux uropathy proteinuria develops through an intermediate mechanism of immune complex glomerulonephritis involving antigenic material of renal tubular epithelium. A patient with a unilateral ureterocele and nephrotic syndrome underwent bilateral renal biopsies during surgical correction of the obstruction. The obstructed kidney showed mild pyelonephritis, but both kidneys showed a glomerulopathy with electron-dense deposits in the mesangial and paramesangial regions associated with positive immunofluorescence for immunoglobulin M (IgM) and the third component of complement (C3). An IgM antibody was eluted from the biopsy specimens and it reacted by indirect immunofluorescence with normal renal tubular epithelium and with the patient's renal tubular epithelium. The eluate also reacted with pre-eluted glomeruli of the patient, but not with normal glomeruli. All antibody activity could be removed from the eluate by pre-incubation with normal kidney. It is concluded that the unilateral renal obstruction produced tubular injury so that as yet unidentified antigens were recognized by the immune system. The resultant antibody response gave rise to circulating immune complexes which were then deposited in glomeruli with subsequent glomerular damage and nephrotic syndrome.

Adult↗
PubMed1980

Remote profunda femoral bypass for limb salvage.

Patients with patency of the distal segment of the profunda femoral arteries can be subjected to a direct end-to-side bypass with either tissue or synthetic grafts to increase blood flow to the lower extremity. The effectiveness and durability of this procedure will be enhanced by patency of the popliteal artery. Diffuse profunda femoris disease, popliteal or tibial peroneal obliterative disease and gangrenous lesions tend to militate against the success of this operation as an isolated procedure without augmenting flow to the distal part of an artery in the leg. Of 18 remote profunda femoris bypasses performed during a four year period, early amputation was required in two patients because of inadequate distal flow and the inability to establish downstream reconstruction. In one patient, an early bypass to the peroneal artery was required following closure of the profunda femoris bypass. The remaining 15 bypasses resulted in limb salvage and significant relief of symptoms. Three patients subsequently required secondary downstream reconstructions. The profunda femoris is surgically accessible for a long length and can serve as an adequate source of blood to the leg and foot in selected patients.

Aged↗
PubMed1978

Construction of a novel plasmid-phage hybrid: use of the hybrid to demonstrate ColE1 DNA replication in vivo in the absence of a ColE1-specified protein.

A hybrid bacteriophage, P420, was constructed in vitro; it contains part of bacteriophage P4 and a 3.6-kilobase derivative of plasmid ColE1. In Escherichia coli, the plasmid-phage hybrid can exist as a stable plasmid or can be packaged into infective bacteriophage particles. Replication of P420, directed by the ColE1 replicon, was found to occur after P420 phage infection of E. coli cells that had been incubated in the presence of chloramphenicol. Replication began without a lag period and resulted in the synthesis of covalently closed circles of P420 DNA. Like ColE1 DNA replication but unlike that of P4, replication was dependent on DNA polymerase I and was sensitive to rifampicin. The presence of a resident ColE1 plasmid in the infected cells resulted in an inhibition of the replication of the incoming P420 DNA. These results indicate that ColE1 does not require a plasmid-coded protein to replicate its DNA in vivo and demonstrate the utility of P4 bacteriophage for coupling bacteriophage properties to a plasmid replicon.

Bacterial Proteins↗
PubMed1977

D-Amphetamine thermal effects, metabolic rate and motor activity in rats.

The effect of d-amphetamine-induced hypothermia among rats maintained at a cold ambient temperature is related to its ability to release dopamine in the dopaminergic neurons in the mesolimbic pathway. However, the physiological mechanisms which mediate the hypothermia (heat loss or a decrease in heat production) are not known. Since we have failed to demonstrate effects induced by d-amphetamine on food intake or on heat sensors on the rat's tail we conclude that these are not the mechanisms involved in hypothermia. Effects of d-amphetamine on O2 consumption and CO2 production of rats kept at various ambient temperatures were investigated in order to find out if there is any relation between a decrease in body temperature and a decrease in the Basal Metabolic Rate. Neither such relations nor any relations between levels of body temperatures and levels of motor activity were found. The problem of the peripheral mechanisms involved in d-amphetamine-induced hypothermia remain as yet unidentified.

Animals↗
PubMed1976

Thymidine uptake and utilization in Escherichia coli: a new gene controlling nucleoside transport.

A commonly used strain of Escherichia coli K-12 was shown to be deficient in the transport of a number of nucleosides, including thymidine. Thymidine incorporation was unaffected. Strain AB2497 exhibited a strikingly lower thymidine pulse-label incorporation at low (less than 1 mug/ml) thymidine concentrations than do many other strains. The deficiency appeared to be due to mutation in a single gene. This gene, which we designated nup (for nucleoside uptake), is located at 10 to 13 min on the E. coli linkage map. In nup+ strains, the transport of a given nucleoside was relatively insensitive to large excesses of other nucleosides but was competitively inhibited by the same nucleoside. Mutants deficient inthymidine kinase are deficient in thymidine uptake but normal in deoxyadenosine uptake. A two-step model for nucleoside transport is presented in which the first step, utilizing the nup gene product, is a nonspecific translocation of nucleoside to the interior of the cell. In the second step, the individual nucleosides are modified by cellular enzymes (e.g., nucleosides kinases) facilitate accumulation.

Adenosine↗