Search PubMed⌕ Search

Biomedical subjects

M Spector

Publications and source records attributed to M Spector.

At least 55 records · Page 3Linked to original sources
PubMed1981

A mouse homolog to the avian sarcoma virus src protein is a member of a protein kinase cascade.

Recent work has identified a cascade of membrane bound protein kinases in Ehrlich ascites tumor cells. These enzymes, designated PKL, PKS and PKM, are present in both Ehrlich tumor and mouse brain, but the cascade is active only in the tumor tissue. We have now purified a fourth protein kinase, PKF, that is also associated with this cascade. Protein kinase F prosphorylates PKL and is phosphorylated by PKS. The position of this kinase in the cascade is as follows, where the arrows denote phosphorylation: [Formula: see text] The phosphorylation by PKF, like phosphorylation by the other kinases, is at a tyrosine residue and causes the substrate kinase (PKL) to become active. The role of the tyrosine phosphorylation in activating these kinases is described in detail elsewhere. One result of activation of the cascade is the phosphorylation of the beta subunit of the Na+K+-ATPase, which causes inefficient Na+ pumping and is at last in part responsible for the high aerobic glycolysis of Ehrlich ascites tumor cells. By several criteria protein kinase F from Ehrlich cells is homologous to the src gene product (pp60src) from avian sarcoma viruses. Antiserum raised against PKF and sera from rabbits bearing rous sarcoma virus (RSV)-induced tumors quantitatively precipitate the same 60 kd phosphoprotein from cell lysates of three different RSV-transformed cell lines. Both proteins phosphorylate PKL and a 130 kd cytoskeletal protein (vinculin). The tryptic maps of these proteins are closely similar. Both proteins bind specifically to PKL covalently coupled to Sepharose. We used this latter observation to facilitate the purification of pp60 src from RSV-transformed cells.

Amino Acids↗
PubMed1981

Human stones.

Explore the source record for details and available documents.

Adolescent↗
PubMed1981

Screening of solid and porous materials for pacemaker electrodes.

Several different materials, including one which was porous, were studied to assess their properties as pacemaker electrode tips. Leads were implanted in sheep for periods up to one year. Electrical measurements were made during the implant period and histopathological examination performed after sacrifice. Although titanium vapor-deposited carbon, and silver did not lower the chronic stimulation threshold below that of platinum, their electrical characteristics were within generally acceptable limits. Zinc evoked a severe tissue reactions and a high threshold. Porous titanium alloy electrodes demonstrated reduced dislodgement, more frequent attachment and a lower sensing impedance than other electrodes.

Alloys↗
PubMed1981

Radionuclide bone imaging of femoral prostheses with porous coatings.

Radionuclide bone imaging can be of value in assessing the osseous changes around porous-coated femoral prostheses. Scintimetry appears to be a promising method for determining if radiodensities seen in radiographs of long-term prostheses are indicative of accelerated bone turnover or represent stable osseous structures. In dogs, the periosteal reaction which often occurs within two months of joint surgery masks endosteal-intramedullary osseous changes, including bone ingrowth into the porous coating.

Animals↗
PubMed1981

Developmental aspects of calcium oxalate tubular deposits and calculi induced in rat kidneys.

We employed an experimental hyperoxaluric protocol involving the administration of 1 per cent ethylene glycol drinking water to rats to determine (i) the location and mechanism of retention of renal tubular calcium oxalate crystals, and (ii) how this tubular deposition is modified by magnesium deficiency and contributes to stone formation. Calcium oxalate monohydrate deposition was found predominantly within the lumina of proximal tubules, and was markedly accelerated by magnesium deficiency. Sheet- and strandlike mucoid appearing material attached the crystals to the luminal surface of the renal tubules. The structure of stones found in the renal pelvis suggested that tubular deposits aggregate to form the nidus of the calculus.

Animals↗
PubMed1980

Phosphorylation of the beta subunit of Na+K+-ATPase in Ehrlich ascites tumor by a membrane-bound protein kinase.

We have shown previously that proteoliposomes reconstituted with purified Na+K+-ATPase from Ehrlich ascites tumor cells, transport Na+ with low efficiency (Spector, M., O'Neal, S. and Racker, E. (1980) J. Biol. Chem., 255, 5504-5507). We now present evidence that this low efficiency (expressed in the ratio of Na+-transported/ATP-hydrolyzed) is caused by the phosphorylation of the beta subunit of the Na+K+-ATPase by an endogenous protein kinase. On addition of [gamma-32P]ATP, crude tumor plasma membrane preparations phosphorylated the beta subunit of the ATPase, whereas crude mouse brain plasma membranes did not. However, solubilized Na+K+-ATPase from either tumor or brain wre phosphorylated by purified protein kinase from the tumor plasma membrane and dephosphorylated by a phosphatase. In both cases, the phosphorylated enzyme was inefficient; the dephosphorylated enzyme was efficient after reconstitution into liposomes. During isolation of the Na+K+-ATPase from Ehrlich ascites tumor or mouse brain, an endogenous protease partially cleaved from the beta subunit a polypeptide of 29,000 daltons that contained the phosphorylation site. The proteolytic cleavage of the beta subunit was partially inhibited by phenylmethylsulfonyl fluoride and the major site of phosphorylation was then seen in the 53,000-dalton beta subunit of the enzyme. The isolated 29,000-dalton polypeptide from mouse brain ATPase was phosphorylated by tumor protein kinase with a stoichiometry of 1 mol of phosphate/mol of protein. When this 29,000-dalton polypeptide from mouse brain was incorporated into the tumor Na+K+-ATPase after mild proteolytic digestion, a marked increase in efficiency was observed after reconstitution of the Na+ pump.

Animals↗
PubMed1980

Reconstitution of the Na+K+ pump of Ehrlich ascites tumor and enhancement of efficiency by quercetin.

Plasma membranes from Ehrlich ascites tumor cells were solubilized by octylglucoside in the presence of phospholipids. The Na+K+-ATPase was purified from this extract by adsorption and elution from thio-Seph-arose 4B. The enzyme (specific activity, 7 mumoles of ATP hydrolyzed min-1 mg of protein -1) was reconstituted into liposomes by the octyglucoside dilution procedure. An ATP-dependent Na+ influx with low efficiency was observed. On addition of appropriate amounts of quercetin, the Na+ flux/ATP hydrolysis ratio was increased from 0.4 to 1.4.

Animals↗
PubMed1980

Hemopoiesis in demineralized bone allografts.

Demineralized allogeneic bone matrix (DBM), implanted in muscle, induces the formation of an ossicle within which histologically recognizable hemopoietic tissue develops. Analyses of rabbit ossicle marrow in a methylcellulose culture system demonstrated the presence of committed hemopoietic precursors; colony-forming units in culture (CFUC), erythroid colony-forming units (CFUE) and erythroid burst-forming units (BFUE) by six weeks post-implantation. The time courses of colony and burst formation by progenitor cells of ossicle and femoral marrow were similar. Induction of hemolytic anemia by phenylhydrazine hydrochloride at six weeks post-DBM implantation showed that the ossicle marrow was responsive to systemic erythropoietic stimuli. The DBM implant may provide a unique model for studying the development of hemopoietic microenvironments within bone.

Animals↗
PubMed1979

Characteristics of tissue growth into Proplast and porous polyethylene implants in bone.

(1) Bone does not form within internal pores of undistorted Proplast implants because of the small interconnecting pore size of the material; (2) the nonosseous, fibrous tissue which exists in the pores of Proplast implants in bone is not attached to the surrounding bone (i.e., Sharpey's fibers are not present). The load-bearing support which can be afforded by Proplast implants is limited by the incomplete bone ingrowth along the margins of the material and the tensile strength of Proplast.

Absorptiometry, Photon↗
PubMed1979

Porous titanium endosseous dental implants in Rhesus monkeys: microradiography and histological evaluation.

Artificial tooth roots with porous surface coatings were fabricated by sintering spherical powder of titanium alloy to solid cylindrical cores. The tooth roots were implanted subgingivally in healed mandibular premolar extraction sites of fifteen Rhesus monkeys. Supracrestal abutments were screwed into pretapped holes in the superior aspect of the primary subgingival stage four to eight weeks after implantation of the root. Clinical evaluations were performed monthly. Ten animals were sacrificed for histological evaluation of the functioning free standing implants. Of twenty-nine implants placed, three were lost and four were rated failures on the basis of histological evaluation. Postmortem evaluations revealed bone growth into the porous surface coating of the primary stage of all the implants. The most characteristic features which could be used to describe differences in the implant histology were the buccal and lingual crestal bone heights measured in relation to the root porosity. Twelve of sixteen implants had crestal bone heights within one millimeter of the superior aspect of the root. Four other implants displayed excessive bone recession, revealing as much as one half of the root porosity supracrestally. The four implant failures could be related to unfavorable features of recipient bone sites. The results demonstrate that the bone growth into the porous surface coatings of artificial tooth roots is an efficacious method of dental implant fixation.

Alloys↗
PubMed1979

Porous titanium tooth roots: clinical evaluation.

1. An inert porous vehicle can be successfully used to attach endosseous dental implants to surrounding alveolar bone. 2. Implant size and the width of keratinized gingiva surrounding the implant are critical to the success of the implant. 3. Radiography and pocket depth are useful indicators of the status of porous endosseous roots, while mobility is not.

Alveolar Process↗