Canadian journal of biochemistry最新文献

The pathways leading to the formation of phosphatidylethanolamine in isolated hamster hearts were investigated. The contributions of the CDP-ethanolamine and the base exchange pathways were studied by perfusion with [3H]ethanolamine. The radioactivity of ethanolamine in the heart reached a maximum at 5 min of perfusion and remained constant throughout the perfusion period. Maximum labeling of phosphoethanolamine occurred at 25 min of perfusion and labeling of CDP-ethanolamine did not reach a maximum over the 30-min-perfusion period. Incorporation of radioactivity into phosphatidylethanolamine was marked by a lag during the first 15 min of perfusion, after which a linear increase was observed. This initial lag suggests the minor contribution of the base exchange pathway, as compared with the CDP-ethanolamine pathway. The CDP-ethanolamine pathway was estimated to contribute 290 nmol x min-1 x g heart-1 to total phosphatidylethanolamine formation in hamster heart. Phosphatidylethanolamine formation via decarboxylation of phosphatidylserine was studied by perfusion of hamster hearts with labeled serine. The contribution of this pathway was estimated to be 9.0 nmol x min-1 x g heart-1. Hence, it was concluded that phosphatidylethanolamine was synthesized by all three known pathways and the CDP-ethanolamine pathway was the major pathway for phosphatidylethanolamine biosynthesis in the mammalian heart. The low activities of phosphatidylserine decarboxylase and base exchange enzyme measured in vitro probably reflect the minor contribution of these two pathways to phosphatidylethanolamine biosynthesis.

Methods were developed for the peptide analysis of individual isoproteins of human apolipoproteins separated on urea-polyacrylamide isoelectric focusing (IEF) gels. After IEF the proteins were fixed in the gel matrix by trichloroacetic acid precipitation. Low molecular weight contaminants, including ampholytes, were removed and the proteins were chemically desialylated. Enzymatic digestions with L-1-tosyl-2-phenylethylchloromethyl ketone - trypsin, chymotrypsin, or with thermolysin were accomplished within the gel matrix. The proteolytically released peptides were analyzed by reverse-phase high performance liquid chromatography. These methods facilitated the comprehensive analysis of protein structural differences between individual isoproteins of apolipoproteins in duplicate with as little as 1-2 nmol of each isoprotein, without the use of radiolabels. Human apolipoproteins A-I, C, and E were analysed by these methods.

The polymerization of winter flounder antifreeze polypeptide (AFP) with glutaraldehyde to increase its antigenicity and the conjugation of the AFP to bovine serum albumin so that the AFP could carry a radioiodine label have allowed the development of a convenient and reliable radioimmunoassay (RIA) for the antifreeze. A seasonal concentration profile of serum AFP as determined by the RIA corresponded closely with its activity profile. Winter serum concentrations of AFP measured by the RIA (7-11 mg/mL) agreed well with antifreeze recovery from Sephadex G-75 chromatography of serum (6-10 mg/mL), but less so with concentration estimates reported from activity measurements (12-25 mg/mL) (Petzel, D. H., Reisman, H. M. & DeVries, A. L. (1980) J. Exp. Zool. 211, 63-69). A small but measurable immunological cross-reactivity was detected between the antiflounder AFP and other fish antifreeze polypeptides. Such cross-reactivity was quite unexpected considering the large compositional and structural differences among the various AFP and its significance remains unclear.

Punch wounds (3 mm) were made in the skin of rats and the animals were killed after 1 or 3 days. Plugs (4 mm) of wounded and unwounded skin were incubated in vitro with [3H]fucose. The labelled plugs were homogenized and subjected to sequential extraction with buffered salt solutions, ethanol-ether, and 8 M urea - 50 mM dithiothreitol (DTT). Nondialysable counts in the extracts and insoluble residue were determined and the incorporation of label by wounded and unwounded skin plugs was compared. Wound plugs showed a greater total incorporation of [3H]fucose. In addition, a greater proportion of [3H]fucose was found in the urea-DTT extracts. The highest specific activity (disintegrations per minute [3H]fucose per milligram dry weight) was found in a finely dispersed precipitate, sedimenting at 10000 x g but not at 1000 x g. The transglutaminase inhibitors aminoacetonitrile and dansyl cadaverine were found to increase the extractability of a portion of the material which incorporated [3H]fucose without affecting the total incorporation. These results show that healing wounds have an increased biosynthetic capacity for an insoluble fucosylated glycoprotein fraction and they suggest that transglutaminase is necessary to make this fraction fully insoluble.

Brown adipose tissue (BAT) of rats is known to grow in response to acclimation to cold. The growth is accompanied by changes in mitochondrial polypeptide composition (an increase in the relative proportion of a polypeptide of molecular weight 32,000, known to be associated with the thermogenic proton conductance pathway). The mediator of the change in mitochondrial polypeptide composition is unknown. The objective of these experiments was to find out whether any of the pituitary hormones might be the mediator. Treatment of rats with growth hormone failed to alter BAT size or mitochondrial polypeptide composition. BAT grew and the change in BAT mitochondrial polypeptide composition occurred in cold-acclimated hypophysectomized rats, maintained on thyroxine and corticosterone to ensure their survival in the cold. It is concluded that none of the pituitary hormones is the mediator for the cold-induced change in BAT mitochondrial polypeptide composition or is required to exert a direct effect on BAT for cold-induced BAT growth to occur. It also seems unlikely that more than a maintenance amount of glucocorticoids is required for normal cold-induced growth of BAT; these hormones are thus also unlikely to mediate the change in BAT mitochondrial polypeptide composition. The requirement for no more than a maintenance amount of thyroxine for BAT growth and for the cold-induced change in BAT mitochondrial polypeptide composition confirms previous conclusions drawn from studies on cold-acclimated thyroidectomized rats.

Tonin, a new serine protease, found in high concentration in rat submaxillary glands, leads to a significant activation of human amniotic fluid renin. The optimum pH on renin activation by tonin was found at pH 6.0. The reaction was time dependent and the initial rate of angiotensin I generation was constant up to 2 h. The two amniontic fluid samples studied showed an increase in renin activity after incubation with tonin to about five times the control level (268 to 1240 pmol x h-1 x mL-1 and 1490 to 7480 pmol x h-1 x mL-1).

We compared the lysyl-tRNA synthetases from normal (Balb/3T3) and murine sarcoma virus-transformed (KA31) mouse fibroblasts. In agreement with several other reports of mammalian systems, the lysyl-tRNA synthetases from these cells occurred in very large postmicrosomal complexes as determined by gel filtration on agarose columns. Arginyl-, isoleucyl-, methionyl-, phenylalanyl-, and tyrosyl-tRNA synthetases also occurred as part of a large complex or complexes. Activity of glycyl- or leucyl-tRNA synthetase was not detected in a complex. The specific activities of arginyl- and methionyl-tRNA synthetases were three- and five-fold higher, respectively, in a complex from KA31 as compared with a complex from Balb/3T3. In contrast, the specific activity of lysyl-tRNA synthetase from the Balb/3T3 complex was 50% higher than that of the KA31 complex. tRNALys obtained from the complexes of Balb/3T3 and KA31 was fractionated into isoacceptors on columns of RPC-5. The relative amounts of lysine isoacceptors in total preparations of tRNA from normal whole cells and in tRNA obtained from the normal enzyme complex were the same. However, two isoacceptors were present in greater amounts and two were present in lesser amounts in the KA31 enzyme complex as compared with lysine isoacceptors in a total preparation of tRNA from KA31 cells.

Conformational changes of amphotericin B in the presence of cholesterol as well as in the presence of bilayer vesicles of phosphatidylcholine with saturated fatty acid chains of various lengths (14 less than n less than 22) have been monitored by circular dichroism (CD). It has been shown that the observed species are not only dependent on such parameters as the cholesterol content of the vesicles, the vesicles' physical state, and the number of amphotericin B molecules per vesicle, but also on the time elapsed after mixing and the thermal treatment of the system, which may create irreversible changes. In particular, heating through the transition temperature (Tc) vesicles containing cholesterol and loaded with amphotericin below Tc leads to the expulsion into the aqueous medium of a cholesterol-amphotericin complex, a phenomenon which affords an explanation for some of the electron paramagnetic resonance and resonance Raman results. It has also been shown by gel filtration, ultracentrifugation, and Tc determination that interaction of amphotericin B with vesicles in the gel state induces fusion or aggregation of the vesicles, which is not the case (or at least weakly) when the vesicles are in the liquid crystalline state. This aggregation is the more rapid the nearer the temperature of the reaction is to Tc. This study confirms the great complexity of events which may occur during interaction of amphotericin B with model membranes and presents some results which complement those of studies performed with other spectroscopic methods.

Antibodies against pyruvate kinase of Neurospora crassa, induced in rabbits, were used to monitor the interaction of ligands with this enzyme. The technique of microcomplement fixation was employed to probe for conformational alterations elicited by binding of substrates (phosphoenolpyruvate (PEP) and adenosine diphosphate), the allosteric activator (fructose 1,6-diphosphate), and the inhibitor (valine). On binding of PEP and valine to pyruvate kinase a pronounced reduction in the extent of complement fixation was observed. The second substrate, ADP, had no effect while FDP elicited a moderate suppression of complement fixation. These results suggest that as a consequence of conformational changes induced by PEP and valine, some antigenic determinants on the surface of pyruvate kinase are rendered inaccessible to the antibodies.