Expressions of endothelin-1, fibronectin, and interleukin-1alpha of human umbilical vein endothelial cells under prolonged culture

We examined human umbilical vein endothelial cells (HUVECs) under prolonged culture by electron microscopy and by light and electron immunocytochemistry including double immunolabeling. Based on the cell area of HUVECs through multiple passages, we divided the cells into first, second, and third stages, which exhibited distinct morphological and immunocytochemical characteristics. During the first stage, HUVECs were polygonal in shape and had already formed the monolayer confluence. During the second stage, they were characterized by an increased number of Weibel-Palade (WP) bodies, which were actively segregated from Golgi cisterns. Endothelin (ET)-1 and von Willebrand factor, an endothelial cell marker, were occasionally colocalized in WP bodies. The increase in WP bodies correlated with high ET-1 concentration in the cultured medium, suggesting that these inclusions are involved in storage and release of ET-1 in a manner indicating a regulatory pathway. During the third stage, fibronectin and interleukin (IL)-1alpha were expressed in HUVECs as well as in multinucleated giant cells, which originated from HUVECs, but WP bodies decreased in number in association with a decrease in ET-1 immunoreactivity and concentration. The foregoing changes in immunoreactivities for ET-1, fibronectin, and IL-1alpha affecting HUVECs under prolonged culture may reflect a senescent process of these cells.

[Progress in research of the blood coagulation system]

Blood coagulation is an amplification system consisting of reactions between enzymes and zymogens. It has been illustrated as a cascade model. However, the exact mechanism by which haemostasis is achieved under physiological conditions remains to be clarified. The solving of structure-function relation of each coagulation factor, analysis of the enzymological characteristics of each reaction, analysis of the regulation mechanism of the reactions and identification of novel factors involved in coagulation reactions contribute to the understanding of this complex system. Based on these findings, some new conceptions of blood coagulation are proposed. In the model introduced in this review, the extrinsic pathway and the intrinsic pathway of the 'classical' cascade model of the blood coagulation system could not be separated, and the suppression of fibrinolysis by TAFI (thrombin activatable fibrinolysis inhibitor) during coagulation reactions is thought to be a critical process for effective haemostasis.

Zinc suppresses apoptosis of U937 cells induced by hydrogen peroxide through an increase of the Bcl-2/Bax ratio

Treatment of human premonocytic U937 cells with 500 microM H2O2 for 1h followed by 4h incubation in fresh medium to allow the cells to execute apoptotic processes caused DNA fragmentation. However, in the presence of 1mM ZnSO4 throughout the incubation, DNA ladder formation was markedly inhibited. Hydrogen peroxide treatment for 1h with or without zinc increased both Bcl-2 and Bax proteins. However, only Bax protein decreased to basal levels in the presence of zinc during the following 4h incubation, resulting in an increase of the Bcl-2/Bax ratio and prevention of apoptosis. Treatment of U937 cells with 1mM ZnSO4 alone also decreased the levels of Bax protein. Furthermore, we observed that zinc completely inhibited the activation of CPP32 by H2O2, while no significant changes of ICE activities occurred with either H2O2 and/or zinc. These results indicate that the suppression of H2O2-induced apoptosis by zinc is mediated through an increase of the Bcl-2/Bax ratio, which occurs upstream from the activation of CPP32.

Prompt activation of telomerase by chemical carcinogens in rats detected with a modified TRAP assay

The maintenance of telomere length is crucial for survival of cells. Telomerase is an RNA-containing reverse transcriptase, which is responsible for elongation of shortened telomeres. Telomerase reactivation has been suggested to be involved in malignant progressions. To study on the involvement of telomerase activation in in vivo carcinogenesis, we first modified the original TRAP assay by changing the primer designs and the labeling method of PCR products to an end-labeling method. Second, we investigated the activation of telomerase in different organs after treatments of rats with various chemical carcinogens. Very early after the beginning of the treatment, telomerase activity in the liver, kidney, and lung was increased. In most cases, telomerase activation occurred in the primary or favorite target organs. The present results suggest that telomerase activation occurs promptly when animals are exposed to chemical carcinogens, which may contribute to in vivo chemical carcinogenesis.

Increases of thrombomodulin activity and antigen level on human umbilical vein endothelial cells treated with asbestos and man-made mineral fibers

The potential influences of crocidolite asbestos fibers and man made mineral fibers (potassium titanate whisker and magnesium sulfate whisker) on a procoagulant system of human umbilical vein-endothelial cells (HUVECs) were investigated by measuring the activity and antigen level of thrombomodulin (TM) on the cell surface. Statistically significant increases in both the TM activity and TM antigen level were observed on HUVECs treated with crocidolite asbestos fibers for 48 h and 72 h compared to untreated cells at low concentrations of the fibers which showed no sign of a cytotoxic effect on the cells. An extensive increase in both the TM activity and TM antigen level was also observed on HUVECs treated with potassium titanate whisker or magnesium sulfate whisker for 48 h and 72 h. A statistical analysis revealed that these fibers had almost the same effects on the increases in both TM activity and the TM antigen level of HUVECs treated with the fibers for 48 h and 72 h, but a treatment of magnesium sulfate whisker at more than 1.25 micrograms/ml for 24 h was slightly more effective in increasing TM activity on HUVECs compared to other fibers (p < 0.05). The [3H]leucine incorporation in HUVECs increased when the cells were treated with crocidolite asbestos or man-made mineral fibers (MMMFs), indicating that the increases in TM activity and the TM antigen level on HUVECs directly exposed to those fibers may not reflect the sole induction of anticoagulant activities, but the general cell damage induced by the fibers.

Brasiliquinones A, B and C, new benz[alpha]anthraquinone antibiotics from Nocardia brasiliensis. I. Producing strain, isolation and biological activities of the antibiotics

New benz[alpha]anthraquinone antibiotics (brasiliquinones A, B and C) with an ethyl group at C-3 were isolated. The producer was identified as Nocardia brasiliensis. The antibiotics were active against Gram-positive bacteria including Mycobacterium sp., but not active against Gram-negative bacteria or fungi. They were also active against multiple drug-resistant P388/ADR tumor cells.

[Isolation of endothelial cells from human umbilical cords and development of low-cost culture medium]

To study the role of endothelial cells in important biological phenomena such as thrombosis and atherosclerosis, it is necessary to have a sufficient amount of endothelial cells. This report shows modified methods to isolate endothelial cells from the human umbilical vein and the components of potent and low-cost culture medium for the cells.

Induction of heat shock protein 70 and nucleolin and their intracellular distribution during early stage of liver regeneration

Our previous work demonstrated a simultaneous induction of Hsp70 and nucleolin mRNA during the prereplicative stage of hepatocytes after partial hepatectomy [Ohmori, H. et al. (1990) Exp. Cell Res. 189, 227-232]. In the present study, changes of intracellular localization of these proteins were examined. Nucleolin, which mainly localized in the nucleus, increased with time and accumulated in the nucleolus around 12-18 h after partial hepatectomy. Hsp70 protein also increased slightly around 6-12 h after the operation. In accordance with this increase, immunohistochemical staining revealed that almost all nuclei of hepatocytes became Hsp70-positive, although Hsp70 was seen to be dispersed throughout the nucleoplasm and nucleolus at all times examined. Next, we isolated a cDNA clone of ribosomal protein (S-17) and examined its behavior. Induction of S-17 mRNA was observed to be essentially similar to that of nucleolin mRNA in regenerating rat liver, although inductions of histone H2A and H4 occurred at a later time, that is, in parallel with DNA synthesis. Furthermore, we observed a simultaneous induction of Hsp70 and nucleolin mRNA by serum-stimulation after serum-depletion in HeLa and IAR-20 (rat) culture cells. These results suggest that the induction of Hsp70, in addition to nucleolin, was not fortuitous but may be involved in the early events of liver regeneration.

Transforming growth factor beta 1 and beta 2 induce down-modulation of thrombomodulin in human umbilical vein endothelial cells

To investigate the effects of transforming growth factor-betas (TGF-betas) on endothelial anticoagulant activity, we assayed thrombomodulin (TM) activity and antigen levels of human umbilical vein endothelial cells (HUVECs) incubated with TGF-betas in vitro. TGF-beta 1 suppressed surface TM activity and surface TM antigen levels maximally 12 h after incubation in dose-dependent manners. TGF-beta 2 was almost equipotent with TGF-beta 1 for the suppression of them. Both TGF-betas suppressed total TM antigen level in HUVECs, and the time course of the suppression was similar to that of the cell surface TM antigen level. The maximal reductions of TM mRNA levels by TGF-betas were observed at several hours ahead of those observed in both surface and total TM antigens levels, suggesting that the TGF-beta-mediated suppression of TM antigen of HUVECs is primarily regulated at the TM mRNA level. Our present work suggests that the down-modulation of TM level induced by TGF-betas in HUVECs contributes in vivo to promoting the thrombogenesis either at the sites of injury of vessel walls, such as atherosclerotic lesions where TGF-beta 1 is released from platelets, smooth muscle cells and monocytes, or at neovascular walls in tumors secreting TGF-beta 2.

Alterations of expression of the cytoskeleton after immortalization of human fibroblasts

Human diploid fibroblasts (HDF) have a limited in vitro lifespan of population doubling level (PDL) 50-70. The molecular mechanism underlying cellular senescence and immortalization is not thoroughly understood. It has been reported that the cytoskeleton has diverse functions and may have a role in growth regulation through association with other cellular components. To shed light on the relationship between functions of the cytoskeleton and senescence or immortalization, we investigated the alterations in gene expression after immortalization and measured the amounts of mRNAs for talin, vinculin, alpha-actinin, tropomyosin 1 (TM1), vimentin, lamin A and C, and alpha-tubulin by slot blot and Northern blot analyses. We found that the mRNAs for vinculin and vimentin were reduced and the mRNA for lamin A was increased in immortalized cells. We also studied the cytoskeletal protein levels and their intracellular distributions by Western blot analysis and immunostaining. Most of the proteins studied behaved in a way similar to the mRNAs through senescence and immortalization. Vinculin, tropomyosins and vimentin showed their altered distributions in immortalized cells.

Cloning of cDNAs with possible association with senescence and immortalization of human cells

Normal human diploid fibroblasts (HDF) have a finite life span in vitro and have been used as a model system for the study of in vivo aging. Little is known about how changes in gene expression may affect the immortalization of human fibroblasts. We looked for cDNA clones whose mRNAs were differentially expressed between mortal senescent SV40-transformed human fibroblasts (B-32) and the immortal counterparts (B-32F) derived from B-32 cells. We identified three cDNA isolates by subtractive differential hybridization with 32P-labeled cDNA probes from B-32 cells and B-32F cells. Nucleotide sequence analysis of these cDNA clones revealed that they were homologous to the human vimentin, a human mitochondrial gene and a human gene of unknown nature. Slot blot and Northern blot analyses demonstrated that the former two were preferentially expressed in senescent B-32 cells and the last one was less expressed in B-32F immortal cells.

Differential responsiveness of normal and simian virus 40-transformed human fibroblast cells to interferon-gamma

The effect of interferon-gamma (IFN-gamma) on epidermal growth factor (EGF) receptor binding and the proliferation of normal and simian virus 40 (SV40)-transformed human fibroblast cells was compared under identical culture conditions. IFN-gamma induced an enhancement of EGF binding to normal cells, whereas it decreased the EGF binding to SV40-transformed cells. Half-maximal enhancement occurred at 72 h after the normal cells were exposed to 10 U/ml of IFN-gamma, and maximal stimulation was obtained at about 10(2) U/ml of IFN-gamma at 72 h. On the other hand, half-maximal reduction was observed for SV40-transformed cells at less than 10 U/ml of IFN-gamma at 72 h, and maximal reduction was obtained at around 10(3) U/ml of IFN-gamma at 72 h. Scatchard analysis indicated that the number of EGF binding sites of normal and SV40-transformed cells was calculated to be 1.6 x 10(5) and 0.88 x 10(5) per cell, respectively, and was little altered by IFN-gamma treatment. The dissociation constant (Kd) of normal cells, however, decreased from 4.5 nM (control) to 2.0 nM (IFN-gamma-treated), while the Kd of SV40-transformed cells increased from 3.6 nM (control) to 17.0 nM (IFN-gamma-treated). The immunoprecipitation of 125I-labeled EGF-bound EGF receptors with anti-receptor antiserum indicated that a 72-h IFN-gamma treatment did not induce a conformational alteration in the EGF receptors of both normal and transformed cells. The DNA synthesis of normal cells was enhanced by EGF, and IFN-gamma treatment potentiated the effect of EGF on DNA synthesis, probably due to the increased binding affinity of EGF to the cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism of the action of IFN-gamma and TPA on the modulation of epidermal growth factor receptors of human amnion cells

We have examined the mechanism of synergistic action occurring between interferon (IFN)-gamma and 12-0-tetradecanoylphorbol-13-acetate (TPA) with respect to the reduction of 125I-epidermal growth factor (125I-EGF) binding to human amnion (WISH) cells [Karasaki Y et al (1989) J Biol Chem 264: 6158-6163]. The cells were treated with protein kinase C (PKC) inhibitors (H7, staurosporine) to investigate the role of PKC in the synergism between IFN-gamma and TPA, since TPA is a strong activator of PKC. The combined effect of IFN-gamma and TPA was blocked by the PKC inhibitor, suggesting that PKC plays an important role in the synergistic action of TPA and IFN-gamma on the inhibition of EGF binding to the cells. The prolonged incubation (24 h) of the cells with TPA resulted in the restoration of EGF binding to the cells. A 24 h treatment of WISH cells with both IFN-gamma and TPA, however, still exhibited greater than 50% inhibition of EGF binding. No PKC activity, however, was observed in the WISH cells treated with both IFN-gamma and TPA for 24 h as well as with TPA alone for 24 h, indicating that IFN-gamma may synergize with the second mediator induced by PKC rather than PKC itself in the reduction of EGF binding to WISH cells. In addition, IFN-gamma showed the synergistic action with calcium ionophores on the reduction of EGF binding to the cells, suggesting that Ca2+ may be one of the second mediators which was induced by TPA and which cooperated with IFN-gamma.

Induction of glutathione-S-transferase and heat-shock proteins in rat liver after ethylene oxide exposure

Defense mechanisms in rat liver against depletion of glutathione (GSH) and cellular injuries induced by ethylene oxide (EO) were studied. Rats were exposed to EO under either high dose (1300 ppm for 4 hr, once) or low dose (500 ppm for 6 hr, three times a week for 6 weeks) conditions. The hepatic content of GSH decreased dramatically after EO treatment, probably due to detoxication of EO. After the high dose treatment the hepatic GSH content fell by 90% of the control values but recovered within 10 to 15 hr. EO reacts directly with a variety of cellular macromolecules but all rats survived the exposure. Since the metabolites of EO are ethylene glycol and GSH-conjugates, the enzymatic activities of epoxide hydrolase and glutathione-S-transferase (GST) were determined. Only GST activity was found to occur after low dose chronic exposure. The defense mechanism at mRNA level was investigated using probes for GST and several heat-shock proteins (hsps). Enhanced accumulation of GST mRNA was detectable during the recovery period of rats after both high and low dose exposure to EO. Interestingly, both hsp32 (less than 40-fold) and hsp90 (less than 3-fold) mRNA increased after high dose exposure but the mRNA level of one of the major heat-shock proteins, hsp70, did not change under these conditions. Diethylmaleate, which is known to be a GSH depleter in liver, induced hsp32 mRNA only in rat liver, while hsp70 and hsp90 mRNA levels did not change when GSH was depleted. These results suggest that individual heat-shock proteins are induced in different ways under unphysiological conditions such as EO exposure.

Cloning and sequencing of viral integration site in human fibroblasts immortalized by simian virus 40

We have analyzed cellular DNA sequences at the viral genome integration site in a human fibroblast cell line VA13 immortalized by simian virus 40 (SV40). The computer analysis of the junctional cellular DNA sequences did not show any homology to the DNA sequences previously reported. This suggests that immortalization by SV40 was not induced by the destruction of any known oncogene or anti-oncogene at the integration site. We did not find the precise substantial sequence homology at the junctional site between the cellular DNA and SV40 DNA, indicating that the recombination mechanism involved does not require precise sequence homology and therefore, SV40 genome was probably not integrated by homologous recombination. Short direct and inverted repeats of 5 to 29 nucleotides were found in the junctional cellular and SV40 DNA. Cellular DNA abutting SV40 DNA was found by the Northern blot analysis to be expressed in diploid human fibroblasts and SV40-transformed cells. The nature of this RNA is now under study.

Translocation of protein kinase C to membranes induced by TNF does not cause the inhibition of EGF binding to human wish cells

Tumor necrosis factor (TNF) caused an inhibition of 125I-labeled epidermal growth factor [( 125I]EGF) binding to its receptors of human amniotic (WISH) cells at 5 min after addition of TNF, which reached a maximal level (60-70% reduction) after 15-30 min and declined thereafter. TNF also induced a translocation of protein kinase C activity from the cytosol to the membrane, which peaked at 45-60 min after addition of TNF and almost returned to basal level at 120 min. Furthermore, prolonged incubation of WISH cells with 12-O-tetradecanoylphorbol 13 acetate (TPA) diminished the TPA effect on the inhibition of EGF binding to the cells due to the desensitization of protein kinase C; however, TNF still reduced the EGF binding to the cells pretreated with TPA for a long time. These results indicate that although TNF causes the translocation of protein kinase C to the membrane, activation of protein kinase C is not required for TNF to induce a decrease in EGF binding to the cells.

Phorbol ester and interferon-gamma modulation of epidermal growth factor receptors on human amniotic (WISH) cells

In this study we report that pretreatment of human amniotic (WISH) cells with interferon gamma (IFN-gamma) in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA) resulted in the down-modulation of epidermal growth factor (EGF) receptors with respect to both receptor number and affinity. Scatchard analysis of EGF binding in the absence of both IFN-gamma and TPA indicated biphasic binding whereas addition of TPA resulted in the loss of the higher affinity class of sites. Pretreatment with IFN-gamma for 24 h enhanced the TPA-induced inhibition of EGF binding whereas IFN-gamma alone had no effect on binding. Protein kinase C (Ca2+/phospholipid-dependent enzyme) was examined as a possible mediator of IFN-induced EGF-receptor modulation; pretreatment of cells with IFN-gamma affected neither the binding of [3H]phorbol 12,13-dibutyrate to membrane or cytosolic fractions nor the protein kinase C activity, suggesting that IFN-gamma pretreatment did not result in translocation or activation of protein kinase C.

Nucleotide sequence analysis of the DNA binding region of the chicken fibronectin gene

We have determined the nucleotide sequence of 2.0 kb EcoRI segment from the clone lambda FC32 of the genomic chicken fibronectin gene, which is called DNA binding domain. This segment overlapped another clone lambda FC36 and contained three exons which were 16, 17 and 18. They were classified as Type III repeat as originally shown in bovine plasma fibronectin. The average homologies of these three exons among the chicken, rat and human fibronectins in amino acid level are very high (87-98%) compared with that (79-88%) of the exons in the cell binding domain, indicating that this region is highly conservative during the evolution.

Genetic analysis of the cell binding domain region of the chicken fibronectin gene

We have determined the nucleotide sequence of the cell binding domain region of the chicken fibronectin gene and analyzed it evolutionaly. We present here the complete nucleotide sequence of 4.3 kb HindIII/EcoRI segment from the clone lambda FC23 of the chicken fibronectin gene. There were five exons in this segment. When we lined up the amino acid of exons 28, 29 and 31, three alignments, known as the Type III repeat, appeared. Tetrapeptide, -RGDS-, called the cell binding domain, existed in the second repeat, coding exon 30. It was presumed that the Type III repeats were composed of two exons in the chicken gene, the same as in the rat and humans. We found repeatedly appearing amino-acid sequences such as -TIT- (three arrays in these Type III repeats) but also found one of the amino acids substituted in the tripeptide in these Type III repeats (seven arrays). We analyzed these repeats from the point of view of evolution. We used three of the nucleotide sequences (12-18 bp) coding such -TIT- repeats as a unit length for comparing the various homologies after dividing the coding region into 56 segments. The mutual homology of the divided segments to each one of three showed 53% on average. On the other hand, the mutual nucleotide homology of the Type III repeat was 44%. This suggested that the Type III repeat may have been developed by frequent duplication of small gene units.

Inhibition of single and double-stranded DNA-dependent ATPase of RecA protein by ATP ribose-modified analogs

The single-stranded (SS) DNA-dependent ATP hydrolysis at pH 7.5 and 6.2 and the double-stranded (DS) DNA-dependent ATP hydrolysis at pH 6.2 by recA protein (no reaction was detectable at pH 7.5) were found to be inhibited competitively by ribose-modified analogs of ATP, 3'-0-anthraniloyl-ATP (Ant-ATP) and 3'-0-(N-methylanthraniloyl)- ATP (Mant-ATP). The Ki values for Ant-ATP and Mant-ATP is SS DNA-dependent hydrolysis were about 8 and 5 microns at pH 7.5 and 12 and 10 microns at pH 6.2. For the DS DNA-dependent hydrolysis, the Ki values for Ant-ATP and Mant-ATP were about 7 and 6 microns. All these Ki values were much smaller than those of ADP which is also a competitive inhibitor for the ATPase activity of the recA protein. Ant-ATP and Mant-ATP caused a reduction in the Hill coefficients for ATP in SS DNA-dependent ATP hydrolysis at pH 7.5 and DS DNA-dependent hydrolysis. These observations showed that the ATP analogs which have a bulky substituent in the ribose moiety of ATP had strong hydrophobic interactions with the ATP binding site on the recA protein and also contributed to the cooperative effect of ATP.

Modulation of epidermal growth factor receptors by human alpha interferon

Treatment of Madin-Darby bovine kidney (MDBK) cells with human interferon (IFN)-alpha 2 at 37 degrees C results in a dose-dependent inhibition of cell growth and a reduction of the subsequent binding of 125I-labeled epidermal growth factor (EGF) at 4 degrees C. Human IFN-beta and -gamma, which exhibit little antiviral and antiproliferative activities on MDBK cells, have little effect on cell growth or the binding of 125I-labeled EGF to these cells. The binding of EGF is decreased after exposure to IFN-alpha for greater than 8 hr. Scatchard analyses of the EGF binding data indicate that a 20-hr exposure period results in a decrease in the apparent number of cell-surface EGF receptors and a reduction in the affinity of EGF for its receptor. The rate of internalization of EGF by MDBK cells does not appear to be affected by IFN treatment.

Inhibition of ATPase activity of the recA protein by ATP ribose-modified analogs

The single-stranded, DNA-dependent ATPase activity of purified recA protein was found to be inhibited competitively by ribose-modified analogs of ATP, 3'-O-anthraniloyl-ATP (Ant-ATP), and 3'-O-(N-methylanthraniloyl)-ATP (Mant-ATP). The Ki values for Ant-ATP and Mant-ATP were around 7 and 3 microM at pH 7.5, respectively. The inhibitions by these analogs were much stronger than that by ADP, which is also a competitive inhibitor for the ATPase activity of the recA protein. The Ki value for ADP is 76 microM. Ant-ATP and Mant-ATP reduced the Hill coefficient for ATP hydrolysis and thus contributed to the cooperative effect of ATP.

Isolation of immunochemically distinct form of cytochrome P-450 from microsomes of tulip bulbs

A highly purified cytochrome P-450 was obtained from the microsomes of tulip bulbs (Tulipa gesneriana L.). The molecular weight (Mr = 52,500) and amino acid composition of this plant cytochrome P-450 are similar to those reported for rat livers. On the contrary, Ouchterlony double diffusion analyses indicated that cytochrome P-450 isolated from tulip bulbs shares no common antigenic determinants with those of 9 other plants, in spite of the presence of comparable contents of cytochrome P-450 and/or trans-cinnamate 4-monooxygenase with tulip bulbs.

The interaction of the fluorescent probe 1-anilinonaphthalene-8-sulfonate with Carlsberg subtilisin

1-Anilinonaphthalene-8-sulfonate (Ans) binds to Carlsberg subtilisin [EC 3.4.21.14] with a large enhancement of its fluorescence intensity and a shift of the emission maximum to shorter wavelength. The present study indicated that one molecule of Ans binds to Carlsberg subtilisin and inhibits the hydrolysis of substrates in a noncompetitive manner. The dissociation constants of Ans-Carlsberg subtilisin complex were 6.5 x 10(-4) M at pH 6.5 and 7.8, respectively, in terms of fluorescence titration, being in accord with the values 5 approximately 8 x 10(-4) M at pH 7.8) obtained from kinetic studies using various substrates. The dissociation constant of N alpha-acetyl-2-(2-nitro-4-carboxyphenylsulfenyl)-L-tryptophan methyl ester (Ac-Trp(NCps)-OMe), which is a competitive inhibitor of the enzyme, however, became 3.3 times greater in the presence of Ans. It was also observed that the fluorescence intensity of the Ans-enzyme complex decreased in the presence of Ac-Trp(NCps)-OMe or N alpha-acetyl-O-trans-p-phenylazobenzoyl-L-tyrosine methyl ester (Ac-Tyr(PABz)-OMe). These phenomena suggest that the Ans binding site is in the vicinity of the active site of the enzyme.

The effect of side chain structure of ester substrates in determining the rate-controlling step in alpha-chymotrypsin-catalyzed hydrolysis

Presteady state and steady state analyses of the alpha-chymotrypsin [EC 3.4.21.1]-catalyzed hydrolysis of three specific ester substrates and three ring-substituted derivatives were carried out to elucidate the effect of hydrophobic interactions due to the different side chains of the substrates on the individual steps of the reaction. Hydrolysis of all the substrates except for N alpha-acetyl-Nin-formyltryptophan methyl ester (Ac-Trp(CHO)-OMe) was controlled by the deacylation rate. In spite of their comparable Ks values, the substrates with small kcat, such as N alpha-acetyltryptophan methyl ester and N alpha-acetyl-2-(2-nitro-4-carboxyphenylsufenyl)-tryptophan methyl ester, characteristically gave Km values one order of magnitude smaller than the others. For the reaction of Ac-Trp(CHO)-OMe, it was ascertained that the deacylation step was not rate-controlling. It is suggested that the acylation step controls the rate in this case.

Interactions of BPN' and Carlsberg subtilisins with peptides containing aromatic amino acids at the C-terminus. Specific rate enhancement due to the secondary enzyme-substrate interaction

The interaction between BPN' or Carlsberg subtilisins and peptides of the type Ac-Glyn-X-OMe (n = 0, 1, 2, 3), where X denotes one of five different aromatic amino acids, was investigated to elucidate the effect of the secondary interaction on catalysis in relation to the nature of the X residue. The increase in interaction upon elongation of the chain was accompanied by a large increase in kcat but with no marked change in Km in all the series of sensitive substrates. The peptides containing 2-(2-nitro-4-carboxyphenylsulfenyl)-tryptophan, however, acted as competitive inhibitors and exhibited an invariant dissociation constant in spite of the different chain lengths. These observations suggest that the secondary enzyme-substrate interaction induces a conformational change in the active site of the enzyme or in the substrate in such a way as to lower the activation energy and to form a stabilized transient complex. In this respect, BPN' and Carlsberg subtilisins are similar to porcine pepsin and Streptomyces griseus protease 1 rather than to alpha-chymotrypsin.

Kinetic specificities of BPN' and Carlsberg subtilisins. Mapping the aromatic binding site

The kinetic specificities of BPN' and Carlsberg subtilisins [EC 3.4.21.14] were examined with various nucleus-substituted derivatives of Nalpha-acetylated aromatic amino acid methyl esters for mapping their hydrophobic binding sites in comparison with that of alpha-chymotrypsin. The Carlsberg enzyme was generally much more reactive than the BPN' enzyme due to the larger kcat value. The fact that the two sutilisins hydrolyzed Ac-Tyr(PABz)-OMe, which is a derivative of tyrosine bearing a planar trans-p-phenylazobenzoyl group at the OH-function, with the smallest Km value showed that these enzymes possess a more extended aromatic binding site than has so far been demonstrated. Ac-Phe(4-NO2)-OMe was remarkable in being hydrolyzed with a particularly large kcat value (5,500 +/- 700 s-1 at pH 7.8 for Carlsberg subtilisin). Ac-Phe(4-NO2)-OMe and Ac-Tyr-OMe were distinguished by Carlsberg subtilisin in terms of kcat but not by BPN' subtilisin, suggesting that the specificity site of the former is more sensitive to a small change in size of substituent than that of the latter. Ac-Trp(NCps)-OMe and Ac-Trp(NCps)-OH were bound to the enzyme's active site but in a competitive manner. A difference in the standard free energies of binding between the two enzymes may indicate that the hydrophobic cleft of Carlsberg subtilisin is somewhat deeper and/or narrower than that of BPN' subtilisin.

Interactions of alpha-chymotrypsin with peptides containing tryptophan or its derivatives at the C-terminus

The interaction between alpha-chymotrypsin [EC 3.4.21.1] and peptide substrate or peptide inhibitor was investigated to determine how the secondary interaction influences the rate of hydrolysis or the binding and whether or not its effect is variable with alteration of the P1 residue which interacts with the specificity determining site of the enzyme. Kinetic analysis was carried out at pH 6.5 and 7.8 for substrates of the type Ac-Glyn-X-OMe and for inhibitors of the type Ac-Glyn-X-OH where X denotes tryptophan or its derivatives. With substrates containing tryptophan or Nin-formyltryptophan, the second-order rate of hydrolysis increases with increase of chain length. With substrates containing 2-(2-nitro-4-carboxyphenylsulfenyl)-tryptophan, however, the rate of hydrolysis decreases with elongation of the chain, due to an increase in Km(app). The corresponding inhibitors behave differently from the other series of inhibitors at pH 6.5. The results indicate that the influence of the secondary interaction on reactivity or binding is related to the structural features of the P1 residue.

Kinetic study of alpha-chymotrypsin catalysis with regard to the interaction between the specificity-determining site and the aromatic side chain of substrates

In order to investigate how changes in the structures of side-chain aromatic groups of specific substrates influence binding and kinetic specificity in alpha chymotrypsin [EC 3.4.21.1]-catalyzed reactions, a number of nucleus-substituted derivatives of the specific ester substrates were prepared and steady-state kinetic studies were carried out at pH 6.5 and 7.8. Ac-Trp(NCps)-OMe was hydrolyzed more readily at low substrate concentration than Ac-Trp-OMe due to its smaller Km(app) value, suggesting that the bulky 2-nitro-4-carboxyphenylsulfenyl moiety interacts with outer residues rather than with those in the hydrophobic pocket and that this interaction increases the binding specificity. Inhibition experiments using the corresponding carboxylate and analogous inhibitors, however, showed that the carboxy group at the para position of the phenyl nucleus of the substituent sterically hinders association with the active site of alpha-chymotrypsin at pH 7.8 but not at pH 6.5. The kcat values of Ac-Trp(CHO)-0Me, Ac-Tyr(3-NO2)-OMe, and Ac-m-Tyr-OMe were much higher than those of the corresponding specific substrates, indicating that derivatives with a substitute as large as a formyl, nitro or hydroxyl group at the xi-position are stereochemically favorable to the catalytic process. Remarkable increases in Km(app) were also observed. The individual parameters for Ac-Dopa-OMe, however, were comparable to those for Ac-Tyr-OMe.