The mechanism for the inhibition of actin-activated ATPase of smooth muscle heavy meromyosin by calponin.

Calponin, an actin-binding protein, inhibited the acto-heavy meromyosin (HMM) MgATPase and lowered the binding of HMM to actin. The amount of calponin bound to actin or tropomyosin-actin was the same when the ATPase was inhibited 80-90%. While the KATPase was diminished only less than 2-fold in the presence of calponin, the Vmax was decreased 6-fold and 2-fold with actin and tropomyosin-actin, respectively. A comparison of the kinetic constants for the ATP hydrolysis obtained in the presence of actin-calponin and tropomyosin-actin-calponin revealed that the tropomyosin augmented the Vmax 5-fold from the inhibited level, but there was no effect on the KATPase.     

Projection of Monte Carlo and molecular dynamics trajectories onto the normal mode axes: human lysozyme

A method is presented to describe the internal motions of proteins obtained from molecular dynamics or Monte Carlo simulations as motions of normal mode variables. This method calculates normal mode variables by projecting trajectories of these simulations onto the axes of normal modes and expresses the trajectories as a linear combination of normal mode variables. This method is applied to the result of the molecular dynamics and the Monte Carlo simulations of human lysozyme. The motion of the lowest frequency mode extracted from the simulations represents the hinge bending motion very faithfully. Analysis of the obtained motions of the normal mode variables provides an explanation of the anharmonic aspects of protein dynamics as due first to the anharmonicity of the actual potential energy surface near a minimum and second to trans-minimum conformational changes.     

Cloning and nucleotide sequence of the ispA gene responsible for farnesyl diphosphate synthase activity in Escherichia coli

The molecular cloning and the determination of the nucleotide sequence of the ispA gene responsible for farnesyl diphosphate (FPP) synthase [EC 2.5.1.1] activity in Escherichia coli are described. E. coli ispA strains have temperature-sensitive FPP synthase, and the defective gene is located at about min 10 on the chromosome. The wild-type ispA gene was subcloned from a lambda phage clone containing the chromosomal fragment around min 10, picked up from the aligned genomic library of Kohara et al. [Kohara, Y., Akiyama, K., & Isono, K. (1987) Cell 50, 495-508]. The cloned gene was identified as the ispA gene by the recovery and amplification of FPP synthase activity in an ispA strain. A 1,452-nucleotide sequence of the cloned fragment was determined. This sequence specifies two open reading frames, ORF-1 and ORF-2, encoding proteins with the expected molecular weights of 8,951 and 32,158, respectively. A part of the deduced amino acid sequence of ORF-2 showed similarity to the sequences of eucaryotic FPP synthases and of crtE product of a photosynthetic bacterium. The plasmid carrying ORF-2 downstream of the lac promoter complemented the defect of FPP synthase activity of the ispA mutant, showing that the product encoded by ORF-2 is the ispA product. The maxicell analysis indicated that a protein of molecular weight 36,000, approximately consistent with the molecular weight of the deduced ORF-2-encoded protein, is the gene product.     

Identification of 2Fe-2S cysteine ligands in putidaredoxin

The iron-sulfur center of putidaredoxin is coordinated by four cysteine sulfhydrals. In order to determine which of the six cysteine residues in the protein coordinate the Fe-S center, we have individually mutated cysteine residues 73, 85 and 86 into serines. Of these mutant proteins, only C85S and C73S express holo-protein as evidence by SDS-PAGE and EPR spectroscopy. This leads us to the conclusion that residues 39,45,48, and 86 are the cysteines that coordinate the iron-sulfur center in putidaredoxin.     

Experimental stomach-ulcer on pika

Experimental gastric ulcer formation was performed in the pika and compared with that in the rat. Gastric ulcers were formed in pika that were subjected to water restraint for 4-5 days for 2 hours each day. Gastric ulcers were also formed under conditions of 1-4 days for 3 hours each day and 1-2 days for 5 hours each day. The severest (widest) ulcers were obtained under the condition of 5 hours' water restraint. Histopathologically, the ulcers were mostly erosions, but those formed under 5 hours' restraint reached the tunica muscularis mucosae. In addition, inflammatory changes were recognized. In contrast, while gastric ulcers in the rat formed within a short time, they were histopathologically less severe than those in the pika. Therefore, water restraint for 4 hours performed 4-5 times is suitable to obtain gastric ulcer formation in the pika and may result in more severe gastric ulcers than in the rat. Compared with the rat, the pika showed differences in the appearance and degree of gastric ulcers formed by the injection of serotonin and reserpine.     

Microquantification of cholesterol and cholesteryl esters in rat peritoneal macrophages by reverse-phase high-performance liquid chromatography

A simple and rapid method for the microquantification of cholesterol and cholesteryl esters by reverse-phase high performance liquid chromatography has been established. Comparison of elution patterns of authentic cholesterol and cholesteryl esters revealed that a mu Bondasphere reverse-phase C8 (300-A) column was more suitable than a corresponding reverse-phase C4 or C18 column in terms of rapidity and sensitivity. Recovery of cholesterol and cholesteryl esters from a C8 column was greater than 98% when determined either by radioactive cholesterol and cholesteryl oleate or by cholesteryl heptadecanoate. The sensitivity of the quantification ranged from 5 ng to 50 micrograms for both cholesterol and cholesteryl esters. This method was applied to determination of cellular cholesterol and cholesteryl esters of rat peritoneal macrophages. Lipid extracts of these cells were found to contain 38.01 +/- 2.60 micrograms of cholesterol and 3.18 +/- 0.36 micrograms of cholesteryl esters per milligram of cell protein. When the cells were loaded with cholesteryl esters by incubation for 24 h with various concentrations of acetylated low-density lipoprotein, a cellular level of cholesteryl esters showed a dose-dependent increase and reached a maximal level of 106.60 +/- 3.05 micrograms/mg cell protein. Thus, the present method is useful for the microquantification of cholesterol and cholesteryl esters from lipid extracts of biological samples.     

Salmon calcitonin-induced stimulation of 1 alpha,25-dihydroxycholecalciferol synthesis in rats involving a mechanism independent of adenosine 3'':5''-cyclic monophosphate.

The effect of natural salmon calcitonin on accumulation in plasma of 1 alpha,25-dihydroxy-[3H]cholecalciferol from 25-hydroxy[3H]cholecalciferol in vivo was investigated in vitamin D-deficient thyroparathyroidectomized rats into which graded doses of the hormone were continuously infused by use of a balance study system. A dose-dependent increase in plasma concentrations of 1 alpha,25-dihydroxy[3H]cholecalciferol was observed with calcitonin infusion for 6--30h at a rate greater than 20 M.R.C. m-units/h. Infusion of parathyrin or cyclic AMP produced a similar stimulation [Horiuchi, Suda, Takahashi, Shimazawa & Ogata (1977) Endocrinoly 101, 969--974], but the maximal effect of calcitonin was additive to that of either parathyrin or cyclic AMP. Furthermore concurrent infusion of theophylline (0.5 mumol/h) did not potentiate the effect of submaximal doses (3 and 20 M.R.C. m-units/h) of calcitonin. Plasma concentrations of calcium showed a decrease with calcitonin infusion for 30h, but those of Pi remained unchanged. These results strongly suggest that the rat kidney is endowed with a calcitonin-sensitive 1 alpha-hydroxylase system that is separate from the parathyrin/cyclic AMP system and is independent of changes in plasma Pi.     

Formation of hypsorhodopsin in frog retina

Hypsorhodopsin was formed in frog retina by irradiation at liquid helium temperature and converted into bathorhodopsin above about 29 K.     

The structure and function of acid proteases. VI. Effects of acid protease-specific inhibitors on the acid proteases from Aspergillus niger var. macrosporus.

1. The Type B acid protease from Aspergillus niger var. macrosporus was inactivated by reaction with diazoacetyl-DL-norleucine methyl ester (DAN), DL-1-diazo-3-tosylamido-2-heptanone (DTH), and L-1-diazo-3-tosylamido-4-phenyl-2-butanone (DTPB) in the presence of cupric ions. The reaction with DAN took place with 1:1 stoichiometry. The enzyme was also inactivated by reaction with 1, 2-epoxy-3-(p-nitrophenoxy)-propane (EPNP) with concomitant incorporation of approximately two EPNP molecules per molecule of protein. Moreover, these reactions of DAN and of EPNP were markedly inhibited by pepstatin. These results seem to indicate that, as in the case of porcine pepsin [EC 3.4.23.1] and related acid proteases, the enzyme has two essential carboxyl groups at the active site, one reactive with DAN and related diazo reagents in the presence of cupric ions and the other reactive with EPNP, and that pepstatin binds in the vicinity of these residues. 2. The Type A acid protease from the same mold, on the other hand, was found to be markedly less sensitive to these specific inhibitors. Under conditions where the Type B enzyme was completely inactivated by DAN and related diazo reagents, only partial inactivation of this enzyme occurred. The effect of prior mixing of DAN and cupric ions on the pH profile of inactivation was also different from that for the Type B enzyme. Moreover, the Type A enzyme was not inactivated by EPNP. These results thus indicate that the nature of the active site of the Type A enzyme is rather different from that of the Type B enzyme and hence that the Type A enzyme belongs to a different class of acid proteases from the Type B enzyme.