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A Saeed

Publications and source records attributed to A Saeed.

At least 37 records · Page 2Linked to original sources
PubMed1995

Identification and evaluation of the role of endogenous tyrosine kinases in azoxymethane induction of proliferative processes in the colonic mucosa of rats.

Although tyrosine kinases (Tyr-k) are known to play a role in regulating proliferation of normal, preneoplastic and neoplastic cells, little is known about the identity of different species of Tyr-k involved in this process. Utilizing a non-denaturing polyacrylamide gel electrophoresis system, in which the separated proteins from tissue extracts are assayed directly for Tyr-k, we attempted to identify the species of Tyr-k that may be involved in azoxymethane (AOM) induction of colonic mucosal ornithine decarboxylase (ODC) activity, an enzyme whose activity is known to rise in rapidly proliferating cells. We have observed that 5 days after a single injection of the colonic carcinogen AOM (20 mg/kg body wt) to 3-4-month old rats, a significant 230% rise in colonic mucosal proliferative activity (as evidenced by 5-bromo-2'-deoxyuridine (BrdU) immunoreactivity) was also accompanied by a 550% increase in ODC activity. This was also associated with a marked rise (140-240%) in the relative activity of Tyr-k of three mucosal proteins with MI of 165, 145 and 125 kDa. Since the molecular mass of one of the Tyr-k (165 kDa) corresponded to that of EGF-receptor (EGF-R), this led us to examine the role of EGF-R Tyr-k in AOM induction of colonic mucosal ODC. We observed that a 320% increase in mucosal ODC activity, 5 days after AOM injection, was accompanied by over 200% rise in Tyr-k activity of EGF-R. Daily injection of tyrphostin (300 micrograms/kg body wt.), a Tyr-k inhibitor with a higher specificity for EGF-R Tyr-k, significantly attenuated AOM-induced stimulation of both ODC and Tyr-k activity of EGF-R. Administration of AOM also stimulated the rate of synthesis and secretion of TGF-alpha in isolated colonocytes. In addition, the levels of TGF-alpha and its mRNA in the colonic mucosa were also found to be 100% and 250% higher, respectively, in AOM-treated rats when compared with the controls. We suggest that (a) activation of intrinsic Tyr-k of EGF-R is an important event in AOM induction of colonic mucosal proliferative processes, and (b) this activation is thought to be mediated by TGF-alpha through an autocrine mechanism.

Animals↗
PubMed1995

Environmental polychlorinated biphenyls: acute toxicity of landfill soil extract to female prepubertal rats.

Subsurface soil from a National Priorities List landfill containing about 2.5% polychlorinated biphenyls (PCBs) was extracted and the extract cleaned by Florisil slurry and alumina column chromatography. The refined extract contained 48 mg/mL PCB, mainly trichlorobiphenyls and tetrachlorobiphenyls, traces of polychlorinated naphthalenes, 125 micrograms/mL 2,2-bis-p-chlorophenyl-1,1-dichloroethylene (DDE), and low levels of chlorinated dibenzofurans. The refined extract was dissolved in corn oil and administered intraperitoneally to weanling (day 20) female rats on days 20 and 21; rats were terminated on day 22. Limited data indicated possible hematopoietic effects, including neutrophilia. There were no changes in relative uterus, kidney, or adrenal gland weights between total doses of 3 to 96 mg/kg total PCB. Relative liver weights increased significantly at 36 mg/kg and activities of P450s 1A1 (as ethoxyresorufin O-dealkylase) and 2B (as pentoxyresorufin O-dealkylase) increased at 12 mg/kg and plateaued at 36 (P450 1A1) or 48 (P450 2b) mg/kg. Serum total thyroxine (T4) declined significantly at doses of 36 mg/kg and greater; thyroid follicular epithelial cells were significantly larger within the same dose range, but the follicular colloid area decreased to less than 60% control values at 12 mg/kg and remained at this size through 72 mg/kg. Maximum mobilization of T4 apparently occurred at 12 mg/kg and attenuated measured declines in circulating levels. Even though a large proportion of proven and probable estrogenic chlorobiphenyls (CBs) were present, the lower amounts of more potent antiestrogenic aryl hydrocarbon (Ah) receptor agonists and/or decreased responsiveness because of low serum T4 levels may have antagonized the uterotropic response.

Adrenal Glands↗
PubMed1995

Effect of storage on some constituents of camel serum.

Effects of storage at room temperature (23-25 degrees C) and refrigeration (4-5 degrees C) on various biochemical constituents of camel serum were investigated. Albumin, globulin, calcium, phosphorus, cholesterol, aspartate aminotransferase (AST), alkaline phosphatase (AP) and gamma glutamyltransferase (GGT) did not change over 9 days when stored at 4-5 degree C. At 4-5 degree C, creatinine, iron and glucose in camel sera remained stable for 6 days; total protein for 7 days; and blood urea nitrogen for 8 days. Decreased activities in creatine kinase (CK), lactate dehydrogenase (LDH) and alanine aminotransferase (ALT) were apparent after 1, 6, and 7 days, respectively. At room temperature, total protein, albumin, globulin, calcium and phosphorus were stable throughout the 9 days. Changes in glucose and iron occurred after 3 days. Stability at room temperature for LDH was 1 day; AST, 3 days; GGT and ALT, 6 days; and AP, 8 days. CK activity had already declined by 4 hours and by 9 days, only 34% activity remained.

Animals↗
PubMed1994

3-Amino-5,5-dimethylhexanoic acid. Synthesis, resolution, and effects on carnitine acyltransferases.

The selective inhibition of individual carnitine acyltransferases may be useful in the therapy of diabetes and heart disease. Aminocarnitine (3) is a weak competitive inhibitor (K(i) = 4.0 mM) for carnitine acetyltransferase (CAT), although the N-acetyl derivative 4 is about 165 times more potent (K(i) = 0.024 mM) than 3. Compound 3 is also a potent competitive inhibitor for carnitine palmitoyltransferases 1 and 2 (CPT-1 and CPT-2) (IC50 for CPT-2 = 805 nM). We synthesized 3-amino-5,5-dimethylhexanoic acid (7) and its N-acetyl derivative (8) as isosteric analogs of 3 and 4 that lack the quaternary ammonium positive charge. Like 3 and 4, compounds 7 and 8 were competitive inhibitors of CAT with significantly different potencies, but in this case, 8 (K(i) = 25 mM) was 10 times less potent than 7 (K(i) = 2.5 mM). R-(-)-7 and S-(+)-7 were stereoselective inhibitors of CAT (K(i) = 1.9 and 9.2 mM, respectively). Racemic 7 was a weak competitive inhibitor of CPT-2 (K(i) = 20 mM) and had no effect on CPT-1. These results are consistent with differences among the carnitine-binding sites on carnitine acyl-transferases that may be useful in selective inhibitor design. Furthermore, the data suggest that the quaternary ammonium positive charge of carnitine may be important for the proper orientation of carnitine and its analogs in the binding site.

Aminocaproates↗
PubMed1994

Heterologous expression of human prostatic acid phosphatase and site-directed mutagenesis of the enzyme active site.

Earlier covalent modification experiments indicated that histidine, arginine, and carboxylic acid residues were involved in the catalytic mechanism of the acid phosphatase enzyme from human prostate. The present study utilizes site-directed mutagenesis to evaluate the catalytic importance of 7 residues of human prostatic phosphatase, namely His12, His257, Asp258, Arg11, Arg15, Arg54, and Arg79, which are highly conserved in the sequences of high molecular weight acid phosphatases. Both wild type and mutant enzymes were expressed in the yeast Saccharomyces cerevisiae as fusions to a leader peptide of prepro-alpha-factor, which resulted in the secretion of processed proteins into the culture media. The kinetic parameters of the recombinant wild type enzyme were shown to be effectively identical with those of the native protein. The circular dichroism spectra of wild type and mutant proteins were effectively superimposable. Replacement of His12, which was previously shown to be transiently phosphorylated during catalysis, as well as the adjacent Arg11, both resulted in > 10(4) reductions of enzyme activity. Consistent with a postulated involvement of arginine residues in substrate binding, large reductions in Vmax caused by the R15A and R79A mutations were accompanied by marked increases in Km. However, the mutation R54A had only small effects on kinetic parameters. Essential roles for both His257 and Asp258 were also established. The D258A mutation not only caused larger decreases of Vmax toward p-nitrophenyl phosphate compared to the effect of the H257A mutation, but it also caused the reaction to become more sensitive to the nature of the leaving group. It is concluded that His12 and Asp258 are involved in the formation of the phosphoenzyme intermediate as an acceptor of the phospho group and a proton donor for the substrate leaving group, respectively, while His257 may participate in substrate binding or may facilitate the breakdown of the phosphoenzyme by maintaining the protonated state of the phosphorylated His12 residue.

Acid Phosphatase↗
PubMed1993

Carnitine acyltransferase enzymic catalysis requires a positive charge on the carnitine cofactor.

3-Hydroxy-5,5-dimethylhexanoic acid (HDH) is an analogue of carnitine which differs only in the substitution of a quaternary carbon atom for the quaternary ammonium nitrogen. Thus HDH is isosteric with carnitine but lacks the quaternary ammonium positive charge. Racemic HDH, each of its enantiomers, and the O-acetyl derivative (Ac-HDH) were evaluated as alternate substrates and inhibitors for several carnitine acyltransferases. HDH and Ac-HDH are not substrates for carnitine acetyltransferase (CAT) at concentrations up to 10 mM, suggesting that the positive quaternary ammonium charge on carnitine is essential for CAT catalysis. However, HDH competitively inhibits CAT (Ki = 8.3 mM), carnitine palmitoyltransferase-I (CPT-I) (Ki = 3.6 mM), and CPT-II (Ki = 2.8 mM). Ac-HDH is also a competitive inhibitor of CAT when assayed in the reverse direction (Ki = 4.1 mM). Similarly, R-(+)-HDH and S-(-)-HDH are not substrates for CAT, but they are stereoselective competitive inhibitors (Ki = 20.3 and 7.5 mM for the R and S enantiomers, respectively). Stereoselective inhibition by HDH is even more dramatic with CPT-I, since S-(-)-HDH inhibits CPT-I (Ki = 1.4 mM) but R-(+)-HDH has no effect in concentrations up to 5 mM. As with CAT, HDH is a stereoselective inhibitor of CPT-II, and the Ki values for S-(-)- and R-(+)-HDH are 2.2 and 6.7 mM, respectively. Since the observed Ki values are significantly larger than the Km for carnitine, the positive charge on carnitine must also be important, but not essential, for binding to the carnitine site on carnitine acyltransferases.

Animals↗
PubMed1992

Rat liver low M(r) phosphotyrosine protein phosphatase isoenzymes: purification and amino acid sequences.

Two low M(r) phosphotyrosine protein phosphatases have been isolated from rat liver. The enzymes were previously known as low M(r) acid phosphatases, but several recent studies have demonstrated that this family of enzymes possesses specific phosphotyrosine protein phosphatase activity. We determined the complete amino acid sequences of the two isoenzymes and named them AcP1 and AcP2. Both consist of 157 amino acid residues, are acetylated at the NH2-terminus, and have His as the COOH-terminus. The molecular weights calculated from the sequences are 18,062 for AcP1 and 17,848 for AcP2. They are homologous except in the 40-73 zone, where about 50% of residues are different. This fact suggests that the two isoenzymes are produced by an alternative splicing mechanism. There is no homology between these two isoenzymes and the receptor-like phosphotyrosine protein phosphatases LAR, CD45, human placenta PTPase 1B, and rat brain PTPase-1. AcP1 and AcP2 are also distinct from rat liver PTPase-1 and PTPase-2, since these last enzymes have higher molecular weights. AcP1 differs from AcP2 with respect to (1) substrate affinity and (2) its sensitivity to activators and inhibitors, thus suggesting a their different physiological function.

Acid Phosphatase↗
PubMed1991

Exploring borate-activated electron-rich glyoxals as the arginine-reactivity probes. The reactivities of functionally critical arginines in some representative enzymes.

4-Substituted styrylglyoxals have been synthesized and found to benefit from borate catalysis to serve as highly reactive arginine modifiers. A study of the mechanism in arginine modification has affirmed: (i) the role of electronic effects in modulating the arginine reactivity in alpha-dicarbonyls, (ii) the intermediacy in the reaction of a reversible arginine-alpha-dicarbonyl complex and (iii) the identity of the nucleophilic attack at ketone as the rate determining step in the arginine reaction with arylglyoxals. 4-Methoxystyrylglyoxal and 4-(N,N-dimethylamino)phenylglyoxal were used as the probes in analyzing some representative enzymes for the reactivities of their susceptible arginyls. The susceptible arginyls in lactate and malate dehydrogenases were thus found to be appreciably reactive while those in carboxypeptidase-A and pyruvate kinase were only moderately reactive.

Animals↗
PubMed1990

Structure-activity relationship of antiestrogens. Studies on 2,3-diaryl-1-benzopyrans.

A series of 2,3-diaryl-1-benzopyran analogues substituted at position 4 of 2-phenyl with a hydroxy or pyrrolidinoethoxy residue were synthesized as models for (E)-triarylpropenones constrained in the s-trans conformation. The prototypes, belonging to five chemical series, were evaluated for their estrogen receptor affinity and for estrogen agonist-antagonist activities. The 4H-1-benzopyran-4-one, the 2,3-dihydro-4H-1-benzopyran-4-one, the 4H-1-benzopyran, and the 2,3-dihydro-1-benzopyran derivatives were found to be inactive or only marginally activate as receptor ligands or estrogen agonists-antagonists. In the 2H-1-benzopyran category the parent phenol was also inactive whereas the basic ethers 16 and 26 were modest receptor ligands while being quite active as antiestrogens. In a comparative study the benzopyran 16 was found to be more effective antiestrogen than tamoxifen while being as effective as LY-117018. The benzopyrans have thus emerged as a new class of potent antiestrogens.

Animals↗
PubMed1990

Structure-activity relationship of antiestrogens. Effect of the side chain and its position on the activity of 2,3-diaryl-2H-1-benzopyrans.

A series of 2,3-diaryl-2H-1-benzopyrans carrying a tertiary aminoethoxy chain at the ortho, meta, or para position of 2-phenyl or an alkyl at position 4 of the pyran ring were synthesized and evaluated for their affinity for estrogen receptor (ER) and for microsomal antiestrogen specific binding site and for their uterotrophic-antiuterotrophic activities in rodents. The analogues bearing the side chain at the para position of 2-phenyl were found to be active while those substituted at the meta and ortho positions were inactive as ER ligands as well as estrogen agonists-antagonists. Among para-substituted ethers, the 2-piperidinoethoxy analogue 5 was found to be a more effective antiestrogen than the corresponding pyrrolidino, dimethylamino, and related analogues. Incorporation of a methyl or an ethyl at C4 in the pyran nucleus was found to increase receptor affinity of the prototypes. The ethyl was also found to potentiate agonist activity of the prototype while abolishing its antagonist activity. The piperidino analogue 5 was found to be a better antiestrogen than tamoxifen as well as LY-117018 in rats as well as mice. The prototypes were also found to have high affinity for the microsomal antiestrogen specific binding sites. The benzopyrans have thus emerged as a new group of potent antiestrogens.

Animals↗
PubMed1990

Structure-activity relationship of antiestrogens. Phenolic analogues of 2,3-diaryl-2H-1-benzopyrans.

Phenolic analogues of 2-[4-(2-piperidinoethoxy)phenyl]-3-phenyl-2H-1-benzopyran (1), a novel antiestrogen, were synthesized and evaluated for their structure-activity relationship. Incorporation of OH at position 7 was found to improve receptor affinity of the benzopyran while having no effect on its action as an antagonist. Similar substitution of 2-phenyl as well potentiated receptor affinity as well as antagonist activity of the prototype. The monophenol 19 and the diphenol 25 were thus found to be good receptor ligands, devoid of estrogen agonist activity and associated with marked antiestrogenic activity of comparable order. Both caused nearly complete inhibition of the estradiol stimulated uterine growth in rats as well as mice and were thus found to be better antiestrogens than tamoxifen, trioxifen, and LY-117018. A binding-site model for estrogen receptor rationalizing the structure-activity relationship of benzopyrans in relation to that of the triarylethylene and the triarylpropenone antiestrogens has been discussed.

Animals↗
PubMed1990

Bovine brain low Mr acid phosphatase: purification and properties.

Low molecular weight acid phosphatase from bovine brain was purified to homogeneity using affinity chromatography on p-aminobenzylphosphonic acid-agarose to obtain the enzyme with both high specific activity (110 mumol min-1 mg-1 measured at pH 5.5 and 37 degrees C with p-nitrophenyl phosphate as substrate) and good yields. The enzyme was characterized with respect to molecular weight, amino acid composition, pH optimum, Km and Vmax in varying substrates, and to the Ki of varying inhibitors. Furthermore, transphosphorylation to glycerol was demonstrated by measuring the released p-nitrophenol/Pi concentration ratio during the initial phase of the catalyzed reaction. The enzyme was inactivated by iodoacetate and 1,2-cycloexanedione. Inorganic phosphate, a competitive inhibitor, protected the enzyme from being inactivated by the above compounds, demonstrating the involvement of both cysteine(s) and arginine(s) at the active site of the enzyme. Furthermore, the strong inhibition exerted by pyridoxal 5'-phosphate and the low inhibitory capacity possessed by the pyridoxal 5'-phosphate analogues pyridoxamine 5'-phosphate and pyridoxal, indicate that at least one lysine residue is present at the active site.

Acid Phosphatase↗
PubMed1989

Structure-activity relationship of antiestrogens: a study using triarylbutenone, benzofuran, and triarylfuran analogues as models for triarylethylenes and triarylpropenones.

In a study of the structure-activity relationship (SAR) of antiestrogens use has been made of certain 1,2,3-triarylbutenones, of 2-arylbenzofurans carrying aryl or aroyl substituents at C3, and of 2,3,4-triarylfurans as conformationally constrained models for triarylethylene (TAE) and triarylpropenone (TAP) prototypes. The position-specific contributions of substituents to receptor affinity and to agonist-antagonist profiles were used as aids in characterizing the relative binding orientation of the prototypes. Although most compounds were found to be weak receptor ligands and poorly active in vivo, the following conclusions could be drawn about their SAR: (i) (Z)-TAPs and TAEs interact with the receptor in an analogous manner using the trans-stilbene core, with their agonist-antagonist profiles depending on the nature of other substructures. (ii) Incorporation into the benzofuran framework introduces a stereoelectronic constraint that compromises the normal binding interactions of TAE, as well as TAP, prototypes, resulting in their poor affinities and weak biological activities. (iii) (E)-TAPs can interact with the receptor through their S-cis conformation, but such a binding mode is unlikely to account for their behavior as antagonists.

Animals↗