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Biomedical subjects

U Christensen

Publications and source records attributed to U Christensen.

At least 73 records · Page 4Linked to original sources
PubMed1982

Recanalized umbilical vein in portal hypertension.

Experience with splenoportography suggests that patency of the umbilical vein occurs in about 9% of the patients with portal hypertension. A widely patent umbilical vein might serve as a decompressive portosystemic shunt. Percutaneous transhepatic portography was performed in 107 patients with cirrhosis of the liver and portal hypertension. A patent umbilical vein was found in 28 patients (26%). This finding significantly paralleled the number and size of other collateral veins, apart from gastroesophageal varices. No significant relation was found between umbilical vein patency and portal pressure, extrahepatic shunting, variceal bleeding, or ascites. It is concluded that a large patent umbilical vein does not effectively relieve portal hypertension, prevent gastroesophageal varices, or protect against variceal bleeding or ascites.

Adult↗
PubMed1981

Local blood pressure in chronic leg ulcers.

The local arterial blood supply was evaluated according to clinical criteria in 30 consecutive patients with chronic leg ulcers. Separately, the blood pressure was measured at the ankle level with both strain gauge plethysmography and a Doppler ultrasonic method. In patients with clinical signs of arterial obliterative disease the systolic ankle pressure and the ankle/arm systolic pressure ratio were lower than in patients without such signs. In none of the patients was the local pressure decreased to such a degree that ischemia was the main cause of the ulcer, nor was gangrene imminent. Hence, success or failure of skin grafting or conservative treatment depends primarily on factors other than the nutritive flow, when the perfusion pressure is above 70 mmHg, as in the present study.

Adult↗
PubMed1980

Kinetic studies of urokinase-catalysed hydrolysis of 5-oxo-L-prolylglycyl-L-arginine 4-nitroanilide.

The enzymic properties of urokinase (EC 3.4.21.31) were studied. The kinetic parameters of hydrolysis of 5-oxo-Pro-Gly-Arg-NA were determined in the pH range 5-9, at 25 degrees C and 37 degrees C. The reaction is affected by only one ionizing group of urokinase with pK 7.15 (25 degrees C) and pK 6.82 (37 degrees C). The results indicate that 5-oxo-Pro-Gly-Arg-NA is a good model substrate for studies of the conversion of plasminogen to plasmin. The Km values of the urokinase-catalysed hydrolysis of plasminogen and 5-oxo-Pro-Gly-Arg-NA are of the same order of magnitude. Plasmin catalyses the hydrolysis of 5-oxo-Pro-Gly-Arg-NA, but the Km value is several hundred times that of urokinase. Urokinase is shown not to react with good plasmin substrates, such as Bz-Arg-OEt and D-Val-Leu-Lys-NA, but is linearly competitively inhibited by 6-amino-hexanoic acid and trans-4-aminomethylcyclohexane-1-carboxylic acid.

Catalysis↗
PubMed1980

Tear flow and soft contact lenses.

Tear flow was determined in 14 persons before and after one month of adaptation to a soft contact lens, (Soflens, Bausch & Lomb), by means of a radioactive tracer (technetium, Tc99m, as pertechnetate), a gamma camera and a computer system. The elimination of the radioisotope from the conjunctival sac was diphasic with a significant increase of the fractional turnover rate after the adaptation period in the initial phase with a rapid elimination, but no change in the basal phase with a slower elimination. The fractional turnover rate was also determined with the soft contact lens placed on the cornea after having been pre-soaked in the technetium solution resulting in a value of 0.021 +/- 0.003 min-1 (mean +/- SEM, n = 12). The fractional turnover rate resulting from instillation of the radioisotope on the non-pre-soaked soft contact lens placed in the eye was found to 0.020 +/- 0.004 min-1 (mean +/- SEM, n = 6). In the studies with the soft contact lens in the eye the elimination curves was monophasic and not diphasic as in normal tear flow studies.

Adult↗
PubMed1979

Studies on the nature of the catalytically essential ionizing group of plasmin with pK 8.4.

A fully carbamylated derivative of plasminogen having no free amino groups has been prepared and converted by urokinase to an active enzyme, called carbamyl plasmin A, with a single free NH2-terminal amino group (Val-561). Carbamyl plasmin A was shown to possess a catalytically essential ionizing group having pK 8.6. Carbamylation of the free NH2-terminal amino group of carbamyl plasmin A led to complete loss of catalytic activity. The results of solvent perturbation studies of normal plasmin (EC 3.4.21.7) indicate that the group with pK 8.4 is a neutral acid group. It is suggested that the catalytically essential ionizing group of plasmin having a pK of 8.4 is the alpha-ammonium group of the NH2-terminal Val-561 or the light chain of plasmin, forming an ion pair with a COO- group of an aspartate or glutamate residue.

Carbamates↗
PubMed1979

Steady-state kinetics of plasmin- and trypsin-catalysed hydrolysis of a number of tripeptide-p-nitroanilides.

The steady-state kinetics of plasmin- (EC 3.4.21.7) and trypsin-catalysed (EC 3.4.21.4) hydrolysis of Bz-L-Phe-Val-Arg-pNA, Bz-D-Phe-Val-Arg-pNA, L-Phe-Val-Arg-pNA, D-Phe-Val-Arg-pNA and D-Val-Leu-Lys-pNA were investigated in the pH range 6-9. The pH dependences of the kinetic parameters correspond with the effects of catalytically essential ionizations in the enzymes, except for reactions with L- and D-Phe-Val-Arg-pNA, in which protonation of the NH2-terminal alpha-amino groups (pK = 7.0) shows some inhibitory effect. The reactions of plasmin and trypsin with p-nitroanilides show kc values similar to those normally found with specific ester substrates, indicating that the deacylation steps of the reactions are rate determining.

Anilides↗
PubMed1978

Purification and reaction mechanisms of the primary inhibitor of plasmin from human plasma.

The primary inhibitor of plasmin in human plasma was purified by a four-step procedure involving fractional (NH(4))(2)SO(4) precipitation, ion-exchange chromatography on a column of DEAE-Sepharose CL-6B and affinity chromatography on both a plasminogen-CH-Sepharose 4B column and a column of 6-aminohexanoic acid covalently coupled through the carboxylate function to AH-Sepharose 4B. No impurities in the final preparation could be detected when tested by immunoelectrophoresis against a range of specific antisera or against rabbit anti-human serum. On polyacrylamide-gel electrophoresis the inhibitor preparation showed a single band. The dissociation constant for the inhibitor-plasminogen complex was determined to be approx. 3mum at pH7.8. The reactions of the inhibitor with human plasmin and with bovine trypsin were studied. Comparison of the results obtained confirms the hypothesis previously presented, namely that the reaction of the inhibitor with plasmin involves at least two steps, the initial rapid formation of an enzyme-inhibitor complex followed by a slow irreversible transition to another complex. The results also indicate that the reaction of the inhibitor with trypsin involves just a single, irreversible step, so that this reaction seems to be less complicated than that of the inhibitor with plasmin. The ways in which 6-aminohexanoic acid influences the reactions were studied. The same value for the dissociation constant (approx. 26mum) for 6-aminohexanoic acid is obtained for both its effect on the reaction of the inhibitor with trypsin and for competitive inhibition of trypsin. The inhibitory effect of 6-aminohexanoic acid thus seems to be due to its blocking of the active site of trypsin. In contrast with this, the inhibitory effects of l-lysine and 6-aminohexanoic acid on the inhibitor-plasmin reaction occur at concentrations much too low to affect the active site of plasmin. The possible dependence of the reaction of the inhibitor with plasmin on a second site(s) on plasmin is discussed.

Aminocaproic Acid↗
PubMed1978

Allosteric effects of some antifibrinolytic amino acids on the catalytic activity of human plasmin.

The effects of L-lysine, 6-aminohexanoic acid, and trans-4-aminomethylcy-clohexane-1-carboxylic acid on the catalytic activity of plasmin (EC 3.4.21.7) have been investigated. The kinetics of the plasmin-catlysed hydrolysis of alpha-N-benzoyl-L-arginine ethyl ester in the presence of these compounds have been studied at a number of different concentrations of the three modifiers. They each exert two effects on the reaction, an activation and an inhibition, the concentration dependencies of which are markedly different. They must therefore arise from two different interactions between plasmin and the modifier. The inhibition is competitive, so that it most probably results from direct interaction at the catalytic site. The activation is kinetically non-competitive. The experimental observations seem to be explained best by assuming that L-lysine and certain analogous compounds function as both allosteric modifiers and competitive inhibitors of plasmin.

Allosteric Regulation↗
PubMed1977

Kinetic properties of the primary inhibitor of plasmin from human plasma.

The interaction of human plasmin with the newly discovered alpha2-plasmin inhibitor was investigated. It was found from rate measurements that the reaction involves the rapid formation of a first enzyme-inhibitor complex, followed by the slow irreversible transition to another complex. L-Lysine influences the first step, but not the second.

Fibrinolysin↗
PubMed1977

Kinetic studies of the urokinase-catalysed conversion of NH2-terminal glutamic acid plasminogen to plasmin.

Initial velocities for the urokinase (EC 3.4.99.26)-catalysed conversion of glutamic acid plasminogen to plasmin (EC 3.4.21.7) have been determined at various urokinase and glutamic acid plasminogen concentrations. As has been found for the corresponding reaction with lysine plasminogen this conversion obeys the Michaelis rate equation. The apparent Michaelis constants are of the same order of magnitude for lysine and glutamic acid plasminogens. The difference in conversion rates for the reactions has been shown to be connected with their having different catalytic constants. The data were analysed according to two reaction schemes, in one of which only one peptide bond is split during the glutamic acid plasminogen-plasmin conversion and in the other of which the cleavage of two peptide bonds with the obligatory formation of an intermediate plasminogen is assumed. The results favour the former.

Binding Sites↗
PubMed1977

Kinetic studies of the urokinase catalysed conversion of NH2-terminal lysine plasminogen to plasmin.

A method for determining initial velocities of the urokinase (EC 3.4.99.26) catalysed converstion of NH2-terminal lysine plasminogen to plasmin (EC 3.4.21.7) is presented. This reaction has been coupled with the hydrolysis of alpha-N-benzyoly-L-arginine ethyl ester, which is catalysed by plasmin, and its rate has been determined from the time course of the overall reaction. The proenzyme-enzyme conversion was found to obey the Michaelis-Menten rate equation. The following values of the kinetic parameters were obtained: the apparent Michaelis constant, Km = 40.7 +/- 6.2 muM; the catalytic constant, kc = 2.59+/-0.31 s(-1), and kc/Km = 6.36-10(4) +/- 0.24-10(4) M(-1)-s(-1).

Endopeptidases↗