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Biomedical subjects

B Jacobson

Publications and source records attributed to B Jacobson.

At least 109 records · Page 6Linked to original sources
PubMed1977

Stereotaxic instrument for needle biopsy of the mamma.

A stereotaxic instrument is described which facilitates percutaneous needle biopsy of the breast for microscopic diagnosis. The instrument consists of an x-ray tube mounted on a hinged arm, pivoting stand, patient table, compression device with film holder and scale system, coordinate-controlled puncture device with separate stand, biopsy instrument, and calculator. The sampling site can be located at a precision within +/- 1 mm. The instrument can also be used for positioning of metal and dye indicators for guiding surgery and for postoperative identification of excised tumors.

Biopsy, Needle↗
PubMed1976

Bone mineral content and mechanical strength of the femoral neck.

The bone mineral content of the femoral neck of 61 autopsy specimens was assayed by x-ray spectrophotometry. The mechanical strength of the specimens was also determined experimentally by applying a compressive force perpendicularly to the shaft. The ultimate force at fracture was obtained from force/displacement plots. A coefficient of correlation of 0.89 between bone mineral content of the femoral neck and the ultimate force at fracture was found. Even when limited to a group of women aged 67-80 a fairly close correlation was found. This indicates that the bone mineral level, measured in vivo, can be used as a criterion of the risk of fracture in elderly women.

Age Factors↗
PubMed1975

Isolation of peptides from the carboxyl carrier subunit of transcarboxylase. Role of the non-biotinyl peptide in assembly.

Transcarboxylase is made up of a central hexameric subunit (S20,W similar 12 S), three peripheral dimeric metallo subunits (S20,W similar to 5 S), and six biotinyl carboxyl carrier subunits (S20,W similar to 1.3 S). The results presented here show that the carboxyl carrier subunit is required for assembly of the 12S and 5S subunits into the oligomer. However, only a portion of the subunit is required for assembly. On treatment of transcarboxylase briefly with trypsin at pH 6.3 extremely susceptible peptide bonds of the carboxyl carrier protein are cleaved releasing biotinyl peptides of about similar to 66 and similar to 40 residues. The resulting trypsinized transcarboxylase, though enzymatically inactive, remains essentially intact as judged by its hydrodynamic and molecular sieving properties. The modified enzyme can be dissociated at pH 8 to the central 12S subunit and peripheral 5S subunit to which the residual portion(s) of the cleaved carboxyl carrier protein is still attached. These components can then be separated by molecular sieving. The residual portion of the carboxyl carrier protein (non-biotinyl peptide) can then be isolated by dissociation of the 5S subunit complex at pH 9 and by chromatography over Bio-Gel A-1.5m. The isolated non-biotinyl peptide has been shown to contain the combining domain of the 1.3SE carboxyl carrier protein since it causes combination of the 12S and 5S subunits. Active enzyme is formed by combination of the intact carboxyl carrier protein and the 12S and 5S subunits and an inactive oligomer of similar size is formed if the non-biotinyl peptide is used in place of the carboxyl carrier protein. The similar to 66- and similar to 40-residue biotinyl peptides, which are released by the trypsin treatment, apparently occur on an exposed portion of the enzyme. This portion of the carboxyl carrier protein apparently serves to place the biotinyl group adjacent to the two substrate sites of the enzyme, one of which is on the peripheral subunit and the other on the central subunit. Thus the carboxyl carrier protein has two functions: one portion holds the 12S and 5S subunits in juxtaposition and the other portion orients the biotinyl group adjacent to the substrate sites so that it may function as a carboxyl carrier between the sites.

Acetyltransferases↗
PubMed1975

Evidence that the two partial reactions of transcarboxylation are catalyzed by two dissimilar subunits of transcarboxylase.

The results presented here show that isolated subunits of transcarboxylase specifically catalyze the two partial reactions of transcarboxylation as shown in eq 1-3. The 12S central subunit is active in the transcarboxylation with methylmalonyl-CoA but inactive with oxalacetate and the peripheral metallo 5S subunit is active in the transcarboxylation with oxalacetate but inactive with methylmalonyl-CoA. These subunits, likewise, are specific for the reverse partial reactions; the central subunit catalyzing transfer from the carboxylated biotinyl group to propionyl-CoA to yield methylmalonyl-CoA and the peripheral subunit to pyruvate to yield oxalacetate. Thus, the central subunit contains the sites for the CoA esters (methylmalonyl-CoA and propionyl-CoA) and the peripheral metallo subunits for the keto acids (oxalacetate and pyruvate). In the overall reaction the biotinyl carboxyl carrier protein acts as a shuttle to carry the carboxyl groups between the two subunits. Biotin and certain biotin analogs are inactive in these partial reactions but the similar to 40- or similar to 66-residue biotinyl peptides, which are derived from the carboxyl carrier protein, are active. Transcarboxylase can be reconstituted from its isolated subunits and a comparison was made of the rate of the overall reaction when the subunits were assembled, as in the intact enzyme, with that obtained when the reaction was catalyzed by the nonassembled subunits. In the latter case, since the biotinyl carboxyl carrier subunit must diffuse from one subunit to the other, the overall reaction is much slower than with the assembled subunits. The reaction with trypsinized transcarboxylase from which the similar to 66-residue and similar to 40-residue biotinyl peptides have been stripped, likewise, was slow even though the biotinyl peptides were added to the reconstitution mixture. The 12SH and 5SE subunits remain assembled after trypsin treatment but the biotinyl peptides apparently do not combine firmly or properly with the trypsinized enzyme and the biotinyl group apparently must oscillate as a carboxyl carrier between the two sites on the subunits by diffusion.

Acetyltransferases↗