Replacement of finger and growth factor domains of tissue plasminogen activator with plasminogen kringle 1. Biochemical and pharmacological characterization of a novel chimera containing a high affinity fibrin-binding domain linked to a heterologous protein.

A novel triple-kringle plasminogen activator protein, PK1 delta FE1X, has been produced which is a genetic chimera between the fibrin binding kringle 1 domain of plasminogen and the two kringles and serine protease domains of naturally occurring wild-type tissue plasminogen activator (wt t-PA). This chimera also contains a modification to prevent high mannose type N-linked glycosylation on kringle 1 of t-PA. PK1 delta FE1X is biochemically and fibrinolytically similar to wt t-PA in vitro but retains the decreased plasma clearance rate characteristic of other t-PA variants which lack fibronectin finger-like and epidermal growth factor domains. The serine protease domain of PK1 delta FE1X exhibits the amidolytic activity characteristic of wt t-PA. In an indirect coupled plasminogen activator assay, the specific activity of PK1 delta FE1X is approximately 1.4 times greater than that of wt t-PA. In a fibrin film-binding assay, greater binding to untreated fibrin is observed with wt t-PA than with PK1 delta FE1X. However, following limited plasmin digestion of the fibrin film, PK1 delta FE1X binding increases to the level observed with wt t-PA. The incremental binding to plasmin-digested fibrin observed with PK1 delta FE1X is eliminated if plasmin digestion of the fibrin film is followed by carboxypeptidase B treatment. This result suggests that plasminogen kringle 1 binds plasmin-digested fibrin even after recombination with a heterologous protein. The fibrinolytic activity of PK1 delta FE1X in human plasma clot lysis assays was similar to that of wt t-PA at activator concentrations of approximately 1 microgram/ml. At substantially lower concentrations, approximately 0.1 microgram/ml, PK1 delta FE1X was only slightly less active than wt t-PA. Pharmacokinetic analysis showed that wt t-PA activity is cleared approximately 15 times as rapidly as PK1 delta FE1X following intravenous bolus injection. In a rabbit jugular vein clot lysis model, intravenous bolus injection of 0.06 mg/kg of PK1 delta FE1X showed greater thrombolytic potency than a similar administration of 0.5 mg/kg of wt t-PA. Thus it appears that in vitro exon shuffling techniques can be used to generate novel fibrinolytic agents which biochemically and pharmacologically represent the combination of individual domains of naturally occurring proteins.     

Collagen crosslinks and their relationship to the thermal properties of calf tendons

The hydrothermal isometric tension and thermal transition temperature of collagen were determined in tendons from three different calf muscles. The levels of the nonreducible collagen crosslink, pyridinoline, and the collagen-associated Ehrlich chromogen were also measured in the three tendons. The reducible collagen crosslinks, hydroxylysinonorleucine, dihydroxylysinonorleucine, and histidinohydroxymerodesmosine were measured in two tendons. The thermal properties and levels of crosslinks were found to vary considerably between the different tendons, and also at different sites in two of the tendons. A strong correlation was observed between the thermal transition temperatures and the hydrothermal isometric tensions of the nine tendon sites examined. Both thermal properties correlated with the concentration of both pyridinoline and Ehrlich chromogen. The analogous behavior of the collagen-associated Ehrlich chromogen and the pyridinoline crosslink supports the role of the Ehrlich chromogen as a nonreducible crosslink.     

A spectrophotometric assay of ATP synthesized by sarcoplasmic reticulum.

The problems encountered with a coupled enzyme assay for ATP using glucose, hexokinase and glucose-6-phosphate dehydrogenase are discussed and a modification where fructose and glucosephosphate isomerase were substituted for glucose is described. This modified assay was used successfully to measure the ATP synthesized by reversal of the sarcoplasmic reticulum ATPase. ATP synthesized by adenylate kinase contaminating the sarcoplasmic reticulum was easily corrected for by a subtraction procedure.     

Changes in the fatty acid composition of sarcoplasmic reticulum lipids and calcium uptake activity

Supplementing the diet of rats with saflower oil or hydrogenated coconut oil resulted in marked changes in the fatty acid composition of the skeletal muscle sarcoplasmic reticulum hut did not affect such properties of the sarcoplasmic reticulum as the rate of Ca²⁺ uptake, the total amount of Ca²⁺ taken up, the rate and extent of Ca²⁺ release in the cold, and the basal and extra ATPase activities. Both of the oil supplements resulted in large increases in the proportion of linoleic acid in the sarcoplasmic reticulum hut neither of them significantly affected the proportion of polyenoic to saturated + monoenoic fatty acids. The relisons for the unexpectedly high linoleic acid content in the sarcoplasmic reticulum of the hydrogenated coconut oil supplemented rats are not known.     

Digital Computer Simulation of Respiratory Response to Cerebrospinal Fluid PCO2 in the Cat

The respiratory control system is treated as linear with a transmission delay between ventilation and sensing points (chemoreceptors). To the accepted variables involving body gas stores, ventilatory effects, transmission effects, and steady state pH, P(CO2), P(O2) chemoreceptor response, certain detailed analysis of the central receptors have been added. By construction of a model for medullary CO(2) receptor utilizing expected values of CNS (central nervous system) circulation, CO(2) production, and tissue-buffering effects, results of experimental observation of the effects of alteration of CSF were simulated. The inclusion of CSF effects also allowed simulation of the response to alteration in inspired CO(2), hyperventilation, and the periodic breathing with prolongation of circulation time.     

The biosynthesis of cytokinins in crown-gall tissue of Vinca rosea

The crown-gall tissue of Vinca rosea converts labelled adenine into cytokinins. The principal initial products appear to be ribosylzeatin phosphates; zeatin and ribosylzeatin are also produced in appreciable quantities. The efficiency of conversion of adenine into cytokinins suggests a pathway of synthesis independent of turnover of tRNA. Isopentenyl adenine or its derivatives do not appear to be intermediates in the conversion of adenine to zeatin compounds. Cytokinins in V. rosea turnover rapidly and further metabolism of zeatin derivatives seems to result in their conversion into glucosides which are the main cytokinin active compounds in the tissue.Abbreviations HPLC high performance liquid chromatography - AMP adenosine monophosphate - TLC thin-layer chromatography - GLC gas-liquid chromatography     

Changes in the sarcoplasmic reticulum ATPase protein under denaturing conditions used for sodium dodecyl sulfate--polyacrylamide gel electrophoresis

The electrophoretic pattern of the sarcoplasmic reticulum (SR) ATPase protein was found to change, depending on the conditions used to denature the SR vesicles in sodium dodecyl sulfate (SDS), prior to SDS-polyacrylamide gel electrophoresis. A smearing of the gel pattern above the ATPase protein was observed when the SR vesicles were denatured at 100 °C in SDS, in the absence of β-mercaptoethanol (β-ME). Denaturation of the SR vesicles in SDS at 100 °C in the presence and the absence of β-ME reduced the amount of SR ATPase protein by half. More high-molecular-weight aggregates were formed in the presence than in the absence of β-ME. The other proteins of the SR as well as myofibrils and bovine serum albumin were found to be relatively unaffected by these treatments. It is concluded that, for the study of SR ATPase protein by SDS-polyacrylamide gel electrophoresis, denaturation at 100 °C should be avoided.