Comparison of substrates for measuring cystyl-amino peptidase activity in serum of pregnancy and hepatic disease and in various tissues.
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Biomedical subjects
Publications and source records attributed to T Uete.
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Cystyl-amino peptidase (EC 3.4.11.3) activity in serum or plasma was measured fluorometrically using L-cystine-di-beta-naphthylamide in the absence and presence of thiol such as mercaptoethanol. In the presence of thiol, L-cystine-di-beta-naphthylamide is converted to L-cysteine-beta-naphthylamide, and the enzyme activity to hydrolyze L-cysteine-beta-naphthylamide can be measured, while in the absence of thiol, the enzyme activity to hydrolyze L-cystine-di-beta-naphthylamide is determined. Thiol added did not affect various aminopeptidase activities. The present method is able to measure the enzyme activity hydrolyzing L-cystine-di-beta-naphthylamide and L-cysteine-beta-naphthylamide simultaneously and separately using only L-cysteine-di-beta-naphthylamide. This method is simple, sensitive and useful in clinical routine work, assessing placental function for the evaluation of the pregnant status.
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An autoregulatory system of insulin degradation in the liver in which the rate of insulin metabolism changes in response to fluctuation in its blood levels, was investigated. In the plasma of rats and man in the absence of reduced glutathione (GSH), insulin degradation was not observed, but when a sufficient amount of reduced glutathione was added, the plasma did degrade insulin. This GSH-dependent insulin degrading activity in plasma was quite similar to that in liver in its nature. In rats, this GSH-dependent insulin degrading activity in the liver and plasma was fluctuated in response to fluctuation in the blood insulin levels, and the GSH-dependent insulin degrading activity in plasma was well correlated with that in the liver. Similarly, in man the GSH-dependent insulin degrading activity in plasma was changed in response to fluctuation in the blood insulin levels. In plasma under the physiologic conditions, there is an insufficient amount of reduced glutathione to elicit the insulin degrading activity, but in the liver there is a sufficient amount of reduced glutathione to manifest this activity. This evidence further supports the concept that an autoregulatory system of insulin degradation in the liver exists in man.
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We describe a sensitive, simple, and rapid method for measuring plasmin and plasminogen in plasma, with fibrinogen as substrate. The assay can be done within 1 h. Plasma is diluted 20-fold with buffer and 0.1 ml (5 mul of original plasma) is incubated for 5 min at 37 degrees C, with or without 400 units of streptokinase. Then 2.0 ml of fibrinogen solution is added, the mixture again incubated (37 degrees C, 5 min), and the reaction stopped. The amount of tyrosine liberated from the fibrinogen is measured and is related to activity. This method is suitable for routine clinical work if the same batch of fibrinogen is used.
A simple method is described for the simultaneous determinations of thyroxine and the effective thyroxine ratio (ETR) using a single kit of Thyopac-4. Thyopac ETR values obtained were 1.00 +/- 0.03 for normal subjects; 1.22 +/- 0.11 for hyperthyroid; 0.87 +/- 0.04 for hypothyroid; and 1.02 +/- 0.05 for pregnant women. Cases with TBG deficiency and the nephrotic syndrome indicated normal values. The value (x) was correlated significantly (gamma = + 0.961) with the free Thyopac index (y), representing a regression equation of y = 71.7x(2) - 88.4x + 24.2. Thyopac ETR was shown to be useful in differentiating normal thyroid states from abnormal, irrespective of changes in T(4)-binding globulin (TBG). Further, the T(4) value obtained simultaneously made it possible to detect changes in the TBG level by noting an inconsistent value for the effective thyroxine ratio.
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