Biomedical subjects
Publications and source records attributed to D H Porter.
Intermittent prolapse of a jejunal loop into the gallbladder lumen was observed following cholecystojejunostomy in a patient with advanced carcinoma of the pancreas. This unusual complication was documented by cholangiography and sonography.
We describe a patient in whom thoracic aortography performed following blunt chest trauma revealed what appeared to be a traumatic tear of the proximal descending aorta. As the patient initially refused surgery, aortography was repeated 18 days later, confirming these findings. At thoracic aortotomy the aorta appeared normal; there was no hematoma or tear. We believe this to be the first reported case of false-positive aortography following blunt chest trauma (see Note added in proof).
The computed tomographic and angiographic findings of an isolated external iliac artery aneurysm secondary to cystic medial necrosis in a patient without Marfan's disease are demonstrated. A review of the differential diagnosis and surgical treatment of iliac artery aneurysms is presented. The dramatic surgical sequelae in this patient underscore the importance of preoperative consideration of this rare diagnosis.
A rapid and convenient spectrophotometric assay has been devised to measure proteolysis. The assay is based on the reaction of o-phthalaldehyde (OPA) and 2-mercaptoethanol with amino groups released during proteolysis of a protein substrate. The reaction is specific for primary amines in amino acids, peptides, and proteins, approaches completion within 1 to 2 min at 25 degrees C (half-times of approx 10-15 s), and requires no preliminary heating or separation of the hydrolyzed products from the undegraded protein substrate prior to performing the assay. The OPA assay was relatively as successful as a 2,4,6-trinitrobenzenesulfonic acid (TNBS) procedure in predicting the extent of hydrolysis of a protein substrate. The utility of the OPA method was demonstrated by measuring the degree of proteolytic degradation caused by trypsin, subtilisin, Pronase, and chymotrypsin of various soluble protein substrates. Ethanethiol (instead of 2-mercaptoethanol) or 50% of dimethyl sulfoxide can be included in the assay solution to stabilize certain OPA-amine products. The present method approaches the sensitivity of ninhydrin and TNBS procedures, is more convenient and rapid, and could substitute for these reagents in most assay systems.
The method of quantitating N,N-dimethylglycine involves cation-exchange high-performance liquid chromatography and detection of dimethylglycine with dimethylglycine dehydrogenase. Dimethylglycine was added to plasma and urine and samples were assayed for dimethylglycine. Plasma and urine to which no dimethylglycine was added were also assayed. Recoveries of added dimethylglycine were 99 to 104% with no endogenous dimethylglycine found in rat plasma or normal human urine. The human plasma used contained a small amount of endogenous dimethylglycine. The cation-exchange chromatography separates dimethylglycine from other compounds which can serve as substrates for dimethylglycine dehydrogenase. Repeatability of the assay is +/- 10%. Using this method we have identified dimethylglycine in the urine of a 1-month-old female human patient.
Dimethylglycine dehydrogenase (EC 1.5.99.2) and sarcosine dehydrogenase (EC 1.5.99.1) are flavoproteins which catalyze the oxidative demethylation of dimethylglycine to sarcosine and sarcosine to glycine, respectively. During these reactions tightly bound tetrahydropteroylpentaglutamate (H4PteGlu5) is converted to 5,10-methylene tetrahydropteroylpentaglutamate (5,10-CH2-H4PteGlu5), although in the absence of H4PteGlu5, formaldehyde is produced. Single turnover studies using substrate levels of the enzyme (2.3 microM) showed pseudo-first-order kinetics, with apparent first-order rate constants of 0.084 and 0.14 s-1 at 23 and 48.3 microM dimethylglycine, respectively, for dimethylglycine dehydrogenase and 0.065 s-1 at 47.3 microM sarcosine for sarcosine dehydrogenase. The rates were identical in the absence or presence of bound tetrahydropteroylglutamate (H4PteGlu). Titration of the enzymes with substrate under anaerobic conditions did not disclose the presence of an intermediate semiquinone. The effect of dimethylglycine concentration upon the rate of the dimethylglycine dehydrogenase reaction under aerobic conditions showed nonsaturable kinetics suggesting a second low-affinity site for the substrate which increases the enzymatic rate. The Km for the high-affinity active site was 0.05 mM while direct binding for the low-affinity site could not be measured. Sarcosine and dimethylthetin are poor substrates for dimethylglycine dehydrogenase and methoxyacetic acid is a competitive inhibitor at low substrate concentrations. At high dimethylglycine concentrations, increasing the concentration of methoxyacetic acid produces an initial activation and then inhibition of dimethylglycine dehydrogenase activity. When these compounds were added in varying concentrations to the enzyme in the presence of dimethylglycine, their effects upon the rate of the reaction were consistent with the presence of a second low-affinity binding site on the enzyme which enhances the reaction rate. When sarcosine is used as the substrate for sarcosine dehydrogenase the kinetics are Michaelis-Menten with a Km of 0.5 mM for sarcosine. Also, methoxyacetic acid is a competitive inhibitor of sarcosine dehydrogenase with a Ki of 0.26 mM. In the absence of folate, substrate and product determinations indicated that 1 mol of formaldehyde and of sarcosine or glycine were produced for each mole of dimethylglycine or sarcosine consumed with the concomitant reduction of 1 mol of bound FAD.
Explore the source record for details and available documents.
Bovine skeletal muscle pyruvate kinase was covalently coupled to Sepharose that had previously been activated by low concentrations of cyanogen bromide. Reaction conditions were chosen such that essentially all tetrameric enzyme molecules were covalently bound via a single subunit. Denaturation of the immobilized enzyme with guanidine hydrochloride followed by removal of noncovalently bound subunits amd denaturant resulted in essentially no enzymatic activity remaining bound to the resin. Thus, single immobilized subunits of bovine pyruvate kinase were inactive. Sepharose-bound enzymatic activity could be recovered by adding soluble renaturing enzyme subunits to the immobilized monomers. The former combine noncovalently with the latter, presumably resulting in re-formation of bound tetramers, and an average recovery of 61% of the original matrix-bound activity was observed. While interactions with other enzyme subunits appear to be necessary for catalytic activity of bovine muscle pyruvate kinase, these subunit interactions apparently can be provided by chemically modified subunits. Soluble, renaturing subunits from enzyme that had been inactivated by treatment with trinitrobenzenesulfonic acid were able to interact with matrix-bound single subunits, thereby restoring the enzymatic activity of the latter.
Bovine type M pyruvate kinase can be reversibly denatured by solutions of guanidine-HCl. Subsequent dilution of the enzyme into buffer containing 2-mercaptoethanol or dithiothreitol results in recovery of enzymatic activity with half-times that vary from 185 min at 0 degrees C to 4 min at 45 degrees C. In the temperature range 0-25 degrees C, 90% of the enzymatic activity is recovered. Above about 32 degrees C, the recovery drops off sharply, wih a yield of only 13% at 45 degrees C. Removal of inactive nonspecific aggregates and denatured monomer by gel filtration yields an enzyme with the same specific activity as the starting material. At enzyme concentrations below 3 microns/mL at 16 degrees C or below 25 micron/mL at 7.8 degrees C, the reactivation kinetics show a concentration dependence. At higher concentrations of protein and at temperatures of 16 degrees C or higher, no protein concentration dependence is seen, and the rate of reactivation is described by two first-order relaxations. The rate constants have apparent activation energies of 10.6 and 11.9 kcal/mol. Combinding the results presented here with earlier work from this laboratory [Cardenas, J. M., & Dyson, R. D. (1973) J. Biol. Chem. 248, 6938-6944; Cardenas, J. M., Hubbard, D. R., & Anderson, S. (1977) Biochemistry 16, 191-197] leads to the conclusion that a rapid, major folding produces two species which undergo transconformational steps. This is followed by subunit association which yields the native tetramer.
Explore the source record for details and available documents.
Percutaneous transluminal angioplasty was performed on a right common iliac artery stenosis presumed to be causing renovascular hypertension in a patient with a renal allograft anastomosis to the right external iliac artery. This was complicated by an obstructive dissection resulting in acute threatening renal allograft ischemia. Renal blood flow was restored by means of a transluminal reperfusion catheter until corrective surgery could be performed. This case is reported because such catheters can be acutely helpful to the interventionalist, and they have not been described in the radiology literature.
PURPOSE: Noting a doubling in mortality soon after placement of filters in the inferior vena cava (IVC) from 1985 (7.8%) to 1992 (15.2%), the authors performed a study to define risk factors associated with death soon after IVC filter placement and to develop revised guidelines for filter placement. PATIENTS AND METHODS: During a 4-year period, 141 IVC filters were placed in 137 patients. Patients were divided into two clinical risk groups: those with possible malignancy and those with possible suprainguinal venous thrombus. Survival was monitored for up to 3 weeks after hospital discharge. RESULTS: Death occurred in 16 (26%) of 61 patients with malignancy (P = .0086, compared with patients without malignancy), seven (35%) of 20 patients with suprainguinal venous thrombus (P = .0422, compared with patients without suprainguinal venous thrombus), and six (46.2%) of 13 patients with malignancy and suprainguinal venous thrombus (P = .0091, compared with patients without malignancy or suprainguinal venous thrombus). CONCLUSION: The data indicate that for some patients with malignancy or suprainguinal venous thrombus, insertion of an IVC filter gives little or no survival benefit. A reassessment of IVC filter use in these patients is warranted.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.