Effect of local anesthetics on plasma protein secretion by rat hepatocytes

The effects of some local anesthetics on plasma protein secretion by rat liver slices have been studied and have been compared with those of colchicine. Rat liver slices were pulse-labelled with l-[¹⁴C]leucine for 9 min at 37°C, collected on filter paper, washed with non-radioactive leucine and reincubated in the presence or absence of the drug to be tested. The radioactive plasma proteins produced were obtained by immunoprecipitation from either the chase medium or from the washed slices. Chlorpomazine, (3 · 10^?5 M), dibucaine (10^?5 M), lidocaine (10^?3 M) and procaine (5 · 10^?5 M) inhibited both the synthesis and secretion of plasma protein but did not affect the uptake of l-leucine into the slices nor the incorporation of phosphate into intracellular nucleotide phosphates or into phopholipids. The inhibition of secretion elicited by these drugs is probably not due to the inhibition of protein synthesis since cycloheximide, when added to the chase medium at a concentration which completely inhibits protein synthesis, did not inhibit plasma protein secretion, while cycloheximide plus procaine did inhibit secretion and also caused a retention of non-secreted plasma proteins within the slices. Unlike colchicine, howover, procaine did not cause the retained plasma proteins to accumulate in Goli-derived secretory vesicles, but showed a more general effect causing a distribution among several cell fractions.     

Autocatalytic processing of the streptococcal cysteine protease zymogen: processing mechanism and characterization of the autoproteolytic cleavage sites.

The autocatalytic processing of the streptococcal cysteine protease zymogen (proSCP) to active streptococcal cysteine protease (SCP) was investigated in vitro using purified protein from Streptococcus pyogenes strain B220. It was found that the autocatalytic maturation of the zymogen proceeds through the sequential appearance of at least six intermediates, five of which were characterized through a combination of N-terminal sequencing and MS. Intermediates were identified as resulting from cleavages after Lys26, Asn41, Lys101, Ala112, and Lys118. Time-course studies of the proSCP processing gave a sigmoidal activity profile and indicated that proSCP catalyses its own transformation, mainly via an intermolecular processing mechanism. A similar sequential appearance of intermediates was observed when inactive Cys192Ser proSCP was treated with native, enzymatically active SCP, thus demonstrating that the maturation can exclusively proceed by a bimolecular mechanism. It was shown that proSCP, but not mature SCP, immobilized on a Sepharose resin is capable of liberating itself from the column, indicating that the zymogen is also capable of intramolecular processing. In order to test whether the amino acid sequences at the processing sites could be used for developing new, specific substrates, 3-amino benzoic acid octapeptide derivatives based on all five characterized amino acid sequences from the autoprocessing cleavage sites were synthesized and tested for activity. The 3-amino benzoic acid derivatives have kcat/KM values ranging from 1200 to 7700.M-1.s-1, making them very good endopeptidase substrates for SCP.     

A three-dimensional study of organelle interrelationships in regenerating rat liver. 3. Organelles related to bile.

A number of cell structures are described which show a morphological relationship to the bile canaliculi. Two types of peribiliary vesicles are identified: osmication positive ones occurring between the bile canaliculi and the osmicated immature Golgi cisternae and probably deriving from the latter, and osmication negative ones related to MVB, on which they appear as buds. Small coated vesicles are seen attached to this second type. Large lacunae may originate from MVB, as suggested by the MVB-like internal vesicles they may contain. Some stay in luminal continuity with the bile canaliculi. Canalicular coated vesicles are seen as parts of the canalicular plasma membrane and free in the cytoplasm.     

Delta opioid receptor selectivity induced by conformational constraints in linear enkephalin-related peptides: 1H 400-MHz NMR study and theoretical calculations

Introduction into the structure of the linear hexapeptide DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) or DTLET (Tyr-D-Thr-Gly-Phe-Leu-Thr) of tert-butyl groups as constraints different from cyclization leads to a large increase in the selectivity for delta opioid binding site in the case of DSTBULET [Tyr-D-Ser-(OtBu)-Gly-Phe-Leu-Thr] (Ki delta = 6.14 nM; Ki mu = 374 nM) and BUBU [Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr(OtBu)] (Ki delta = 4.68 nM; Ki mu = 475 nM) or a loss of affinity for DTTBULET [Tyr-D-Thr(OtBu)-Gly-Phe-Leu-Thr] (Ki delta = 866 nM; Ki mu = 4500 nM). This puzzling behavior is studied here by 400-MHz 1H NMR spectroscopy in DMSO-d6 solution and by theoretical calculations. When DSLET and DTLET are compared, the reduction in energetically accessible phi and psi angles induced by the tert-butyl group in the D-Ser2 residue decreases the degree of freedom in the N-terminal part of the peptides. For DSTBULET and BUBU, the rigidification of the backbone evidenced by the appearance of the large NOE's of Phe4 NH-Gly3 alpha and Gly3 NH-alpha and by the loss of the C7 folding around the D-Ser2 residue found in DSLET could explain the drastic loss of affinity for mu opioid receptors. In DTTBULET, a large change in the spatial orientation around the D-Thr2 (OtBu) residue forces the aromatic rings far from each other.(ABSTRACT TRUNCATED AT 250 WORDS)