Signal peptide digestion in Escherichia coli. Effect of protease inhibitors on hydrolysis of the cleaved signal peptide of the major outer-membrane lipoprotein

Upon incubation of the envelope fraction of Escherichia coli a precursor of the major outer membrane lipoprotein that accumulates in the cytoplasmic membrane of the globomycin-treated cell is processed to the mature form [Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712; (1982) J. Biol. Chem. 257, 5177-5182]. When this precursor-containing envelope fraction was incubated in the presence of protease inhibitors such as antipain, leupeptin, chymostatin and elastatinal, a new peptide appeared on a polyacrylamide gel at the position where the signal peptide was expected to appear. This was proved to be the signal peptide of the lipoprotein from the following facts: (a) its appearance is in proportion to the appearance of the lipoprotein and disappearance of the precursor; (b) when the cleavage of the signal peptide from the precursor was inhibited by globomycin, the peptide did not appear on the gel; and (c) the results of labeling of the peptide with [3H]leucine, [35S]methionine and [3H]arginine were consistent with the amino acid composition of the signal peptide. The signal peptide thus accumulated in the envelope fraction was hydrolyzed by an enzyme named 'signal peptide peptidase' when the envelope fraction was washed to remove the inhibitors. The hydrolysis was inhibited by re-addition of these inhibitors. The signal peptide peptidase hydrolyzed the signal peptide only after its cleavage from the lipoprotein precursor.

alpha- and beta-blockade with labetalol in acute myocardial infarction

On the hypothesis that the addition of alpha-blockade would mitigate the haemodynamic disadvantages of beta-blockade alone in the early stages of uncomplicated acute myocardial infarction, 15 patients were studied during the intravenous infusion of labetalol (0.5 mg/kg/h). The mean systemic arterial pressure was reduced by an average of 15 mm Hg. In the nine patients haemodynamically evaluated, the cardiac output (thermal dilution) was reduced without change in the heart rate or left heart filling pressure (pulmonary artery occluded pressure); left ventricular stroke work was significantly decreased. The reduction in these major determinants of myocardial oxygen consumption suggests that the combination of alpha- and beta-blockade may be haemodynamically advantageous in normotensive patients in the early stages of uncomplicated acute myocardial infarction.

An improved method of isolation of rat pancreatic prokallikrein. Characterization of the zymogen and of the kallikrein produced by trypsin activation

A prokallikrein was purified 1600-fold from rat pancreatic tissue in an overall yield of 40% by a simple four-stage procedure. The final and crucial step was immunoaffinity chromatography utilizing antibody raised to a very small amount of prokallikrein. Both the pure zymogen and the active kallikrein generated from it by trypsin activation are single chain species with Mr values of 38400 +/- 300 and 35500 +/- 400, respectively. Valine is the N-terminal amino acid residue of prokallikrein. The zymogen was comparatively stable both to autoactivation and denaturation with respect to temperature and pH. The kallikrein produced by trypsin activation of the zymogen was similar in some of its catalytic properties to the kallikrein purified from autolyzed rat pancreas but the two species differed in their susceptibility to substrate activation.

Mechanism of signal peptide cleavage in the biosynthesis of the major lipoprotein of the Escherichia coli outer membrane

On treatment of Escherichia coli cells with globomycin, a glyceride-containing precursor of the major outer membrane lipoprotein accumulates in the cytoplasmic membrane (Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712). When the envelope fraction from such cells was incubated in a suitable buffer, this precursor could be processed to the mature lipoprotein. The processing involved removal of the signal peptide and subsequent acylation of the NH2 terminus thus bared. Two types of peptidase and an acylation enzyme(s) were found to be involved in these processes. The enzyme that cleaves the signal peptide, called signal peptidase in this paper, had many unique properties: being highly resistant to high temperature, having a wide optimum pH range, and being highly sensitive to detergents. The other peptidase(s), called signal peptide peptidase in this paper, was assumed to be responsible for the digestion of the signal peptide that had been cleaved from the precursor lipoprotein. This enzyme was rather heat-sensitive. Thus the processing from the precursor to the mature lipoprotein at a high temperature resulted in accumulation of a peptide that was most probably the intact signal peptide. The third enzyme(s) involved in the processing was the one that is responsible for acylation of the newly bared NH2 terminus of the lipoprotein. The enzyme activity was also lost at 80 degrees C. In the light of these findings, the biosynthetic pathway of the lipoprotein is discussed.

Mechanism of export of outer membrane lipoproteins through the cytoplasmic membrane in Escherichia coli. Binding of lipoprotein precursors to the peptidoglycan layer

Upon treatment of Escherichia coli cells with globomycin, precursors of Braun's lipoprotein, a peptidoglycan-associated lipoprotein (PAL) and several new species of lipoproteins accumulated in the cell envelope (Hussain, M. Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3012; and Ichihara, S., Hussain, M., and Mizushima, S. (1981) J. Biol. Chem. 256, 3125-3129). The precursors of the Braun's lipoprotein and PAL thus accumulated were able to interact with the peptidoglycan layer. A considerable fraction of the precursor of Braun's lipoprotein was covalently bound to the peptidoglycan layer through its COOH-terminal lysine residue in the same manner as in the mature form. The manner of interaction of the precursor of PAL with the peptidoglycan layer was also the same as that of its mature form in which the central to COOH-terminal region of the lipoprotein is important for the interaction. Both precursors were localized in the cytoplasmic membrane when the outer and cytoplasmic membranes were separated after digestion by lysozyme of the peptidoglycan layer. When the cell envelope fraction was incubated, these precursors were chased to the corresponding mature forms. These results indicate that these proteins can be exported through the cytoplasmic membrane while they still retain the signal peptide that is most probably held in the cytoplasmic membrane.

[Hydrotherapy in swellings with special reference to lymphedema]

Is is to be stated in summary that the majority of positive arguments in the literature publications so far for the application of hydrotherapy in swellings there are weighty counter-arguments especially in lymphatic edema in the narrow sense. The present study (which is only preliminary because of the small number of cases) appears to indicate that these arguments are evidently not so weighty as was assumed hitherto. Even though unfortunately few clinically relevant alterations occurred with hydrotherapy alone, on the other hand, study indicates that we would have to prohibit patients with lymphatic edema from taking cold immersion baths. Hydrotherapy tends to have if anything a favorable influence on the basic psychological condition and according to the data available can be recommended as an additional measure.

Serum immunoreactive trypsin in beta-thalassaemia major

To assess the exocrine pancreatic function in beta-thalassemia major with iron overload, serum immunoreactive trypsin (IRT) was measured in 38 patients with this condition. In 23 (60%) patients' IRT was abnormal: it was subnormal in 16 patients and supranormal in seven. Whereas subnormal IRT concentrations were more frequent in patients of more than 12 years old, supranormal IRT concentrations were more frequent in younger patients. These data provide the first antemortem evidence of exocrine pancreatic damage in this condition. They also suggest that this acinar cell damage is initially associated with a rise in IRT which is followed by a fall in the serum concentration of this enzyme.

Characterization of new membrane lipoproteins and their precursors of Escherichia coli

By labeling cells heavily with [3H]glycerol or [3H]-palmitic acid several new species of lipoproteins, in addition to Braun's lipoprotein and a peptidoglycan-associated lipoprotein called PAL, were found in the envelope of Escherichia coli. The new lipoproteins were immunochemically different from both Braun's lipoprotein and PAL. A strain lacking the structural gene for Braun's lipoprotein contained new lipoproteins and PAL. In addition to Braun's lipoprotein and PAL, four new lipoproteins were found to be localized in the outer membrane, while other two species were found in the cytoplasmic membrane. The localization of one species is unknown. We previously reported that, on treatment of cells with globomycin, a precursor of Braun's lipoprotein accumulated in the cell envelope (Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712). Similarly, the putative precursors of new lipoproteins and that of PAL accumulated in globomycin-treated cells. These precursors contained glycerol and fatty acid(s) as that of Braun's lipoprotein did. It is suggested that the structures of the "signal" region and the mechanisms of processing of all the lipoproteins of E. coli are similar.

Evaluation of coliphages in sewage effluent of Faisalabad

One hundred and ten samples of Sewage were collected from both underground sewage and open drain systems of Faisalabad for coliphage assay. It was observed that the samples from underground sewage system ranged from 8.43 X 10(3)--4.65 X 10(3) in mean plaque forming units (PFU) per ml, whereas the corresponding figures in open drain system varied from 8.66 X 10(3)--3.21 X 10(3) mean PFU per ml. In general, samples from congested areas of both the systems studied tended to be richest both in mean PFU per ml as well as plaque morphological variations. Overall 620 plaque morphological classes were isolated. It was also noted that the mean PFU per ml was higher in the summer than in the winter months and phage contents were increased after rain fall.

Accumulation of glyceride-containing precursor of the outer membrane lipoprotein in the cytoplasmic membrane of Escherichia coli treated with globomycin

The protein accumulated in the cell envelope of Escherichia coli treated with globomycin was identified as the precursor of the outer membrane lipoprotein. The prolipoprotein was almost exclusively localized in the cytoplasmic membrane. The prolipoprotein could be immunoprecipitated with antilipoprotein immunoglobulin and could be chased to the lipoprotein in both in vivo and in vitro. Globomycin inhibited the chase. The prolipoprotein contained glycerol and fatty acid residues, whereas no free sulfhydryl group was detected in it. From these results, it is concluded that the prolipoprotein possesses a glyceride which is covalently bound to the cysteine residue in the peptide as the lipoprotein does and that the removal of signal peptide takes place after the modification. The inhibition of bacterial growth with increasing concentrations of globomycin was accompanied by a gradual increase in the accumulation of the prolipoprotein. Furthermore, growth of the lipoprotein-negative mutant was highly resistant to globomycin. These results strongly indicate that the accumulation of the prolipoprotein in the cytoplasmic membrane causes the death of cells.

Observations of carbon dioxide laser and bone bur in the osteotomy of the rabbit tibia

The tissue responses of a rabbit tibia to superpulse laser osteotomy, continuous-wave laser osteotomy, and bur osteotomy were compared. Healing of the bone occurred after use of all three modalities, but there was a delay in healing after laser osteotomy when compared with bur osteotomy. Laser osteotomy is feasible, but improvements will be needed to make such bone cutting as efficient and controllable as the rotating bur.

Echocardiographic diagnosis of a stuck Bjork-Shiley aortic valve prosthesis

A 55-year-old man who had been asymptomatic after replacement of his aortic valve with a Bjork-Shiley prosthesis, suddenly developed heart failure. The clinical suspicion of prosthetic malfunction was not only confirmed, but specified as being a stuck disc secondary to a large thrombus. Surgical removal of the clot resulted in restoration of normal function and return to the expected findings on echocardiogram. The value of echocardiography in such instances, as well as in routinely following-up patients with prostheses postoperatively, is emphasized.