Evolutionary conservation of the allosteric activation of factor VIIa by tissue factor in lamprey

Essentials Tissue factor (TF) enhances factor VIIa (FVIIa) activity through structural and dynamic changes. We analyzed conservation of TF-activated FVIIa allosteric networks in extant vertebrate lamprey. Lamprey Tf/FVIIa molecular dynamics show conserved Tf-induced structural/dynamic FVIIa changes. Lamprey Tf activation of FVIIa allosteric networks follows molecular pathways similar to human.

SUMMARY

Background Previous studies have provided insight into the molecular basis of human tissue factor (TF) activation of activated factor VII (FVIIa). TF-induced allosteric networks of FVIIa activation have been rationalized through analysis of the dynamic changes and residue connectivities in the human soluble TF (sTF)/FVIIa complex structure during molecular dynamics (MD) simulation. Evolutionary conservation of the molecular mechanisms for TF-induced allosteric FVIIa activation between humans and extant vertebrate jawless fish (lampreys), where blood coagulation emerged more than 500 million years ago, is unknown and of considerable interest. Objective To model the sTf/FVIIa complex from cloned Petromyzon marinus lamprey sequences, and with comparisons to human sTF/FVlla investigate conservation of allosteric mechanisms of FVIIa activity enhancement by soluble TF using MD simulations. Methods Full-length cDNAs of lamprey tf and f7 were cloned and characterized. Comparative models of lamprey sTf/FVIIa complex and free FVIIa were determined based on constructed human sTF/FVIIa complex and free FVIIa models, used in full-atomic MD simulations, and characterized using dynamic network analysis approaches. Results Allosteric paths of correlated motion from Tf contact points in lamprey sTf/FVIIa to the FVIIa active site were determined and quantified, and were found to encompass residue-residue interactions along significantly similar paths compared with human. Conclusions Despite low conservation of residues between lamprey and human proteins, 30% TF and 39% FVII, the structural and protein dynamic effects of TF activation of FVIIa appear conserved and, moreover, present in extant vertebrate proteins from 500 million years ago when TF/FVIIa-initiated extrinsic pathway blood coagulation emerged.

Structural basis for the functions of endogenous angiogenesis inhibitors

Tipping the angiogenic balance between pro- and antiangiogenic stimuli to favor vasculature induction and enhanced angiogenesis is a key event in the growth and progression of tumors. Recently, we demonstrated that the genetic loss of normal physiological levels of individual endogenous inhibitors of angiogenesis leads to a change in the balance between proangiogenic stimulators and their inhibitors, thus favoring enhanced angiogensis and increased tumor growth. Therefore, these endogenous angiogenesis inhibitors provide a physiological threshold against the induction of angiogenesis. The antiangiogenic activities of endostatin, tumstatin, and thrombospondin-1 are evaluated and correlated with their three-dimensional structure and active sites, deriving a structural basis for their activities. Collectively, structural analysis of all three inhibitors demonstrates that the active antiangiogenic sites on these molecules are exposed on the surface and available to bind their putative integrin receptors on proliferating endothelial cells.

Conotoxins and structural biology: a prospective paradigm for drug discovery

Understanding the interactions between activating or antagonizing ligands and their cognate receptors at a molecular level offers promise for the development of pharmacological therapeutics for CNS disorders. The discovery of novel molecules that are capable of discriminating between the varied molecular subunits or isoforms of ion channels should provide a more detailed understanding of the pathophysiology of many CNS disorders. Abundant natural sources of pharmacologically active agents that demonstrate this refined selectivity and specificity are found in the animal toxins of venomous species including: snakes, spiders and the marine snail of the genus Conus. The uniquely fascinating combinatorial ability of the marine snail, genus Conus to modify the pharmacological properties of these neurotoxins or conopeptides within its venom is depicted throughout this review. The myriad of posttranslational modifications and disulfide bonded architectures that have been identified in the conopeptides, are described with an emphasis on the unique pharmacological properties and receptor target specificities that have been ascribed to each of these modifications. The ability of NMR spectroscopy to provide three-dimensional structural information within the interaction interface for both the ligand and target protein following complex formation and its application to conopeptide drug discovery are discussed. Similarly, the strength of merging NMR spectroscopy data with ab initio "restrained soft-docking" for rational pharmacophore design and the identification of lead compounds from in silico library screens will also be discussed. The initial phases of this stratagem are illustrated using two toxin antagonists and the recently determined structure of the KcsA potassium channel. These data exemplify the utility of this approach in elucidating important molecular interfaces of specific toxin-receptor/ion channel complexes, which can be further exploited in drug discovery initiatives.

A new technique for Escherichia coli testing of beef and pork carcasses

A novel technique has been developed to monitor Escherichia coli contamination on carcasses using membrane filtration and m-ColiBlue24 (mCB). mCB is a membrane filtration medium that simultaneously detects total coliforms and E. coli (EC) in a period of 24 +/- 4 h. A study was conducted, using a sponge method to obtain samples from pork carcasses and the excision technique to remove samples from beef carcasses, that compared mCB to standard methods. On pork carcasses (n = 77), the mean values for mCB and violet red bile agar were 7.4 CFU/15 cm2 and 6.1 CFU/15 cm2, respectively. The paired t test (P > 0.05) indicated no significant difference between the two methods (t = 0.5; P = 0.6). Samples from beef carcasses (n = 57) were used to compare mCB to both coliform count and EC Petrifilm. Of these samples, 27 were artificially inoculated with cattle manure. The mean total coliform count was 4.2 log CFU/cm2 and 4.0 log CFU/cm2 on mCB and coliform count Petrifilm, respectively. The mean EC count on mCB was 4.0 log CFU/cm2 and 3.5 log CFU/cm2 on EC Petrifilm. When comparing mCB to both coliform count (t = 2.4; P = 0.02) and EC (t = 3.5; P < 0.01) Petrifilm, paired t tests (P < or = 0.05) indicated significant differences.

Glutamate decarboxylase genes as a prescreening marker for detection of pathogenic Escherichia coli groups

The enzyme glutamate decarboxylase (GAD) is prevalent in Escherichia coli but few strains in the various pathogenic E. coli groups have been tested for GAD. Using PCR primers that amplify a 670-bp segment from the gadA and gadB genes encoding GAD, we examined the distribution of the gadAB genes among enteric bacteria. Analysis of 173 pathogenic E. coli strains, including 125 enterohemorrhagic E. coli isolates of the O157:H7 serotype and its phenotypic variants and 48 isolates of enteropathogenic E. coli, enterotoxigenic E. coli, enteroinvasive E. coli, and other Shiga toxin-producing E. coli (STEC) serotypes, showed that gadAB genes were present in all these strains. Among the 22 non-E. coli isolates tested, only the 6 Shigella spp. carried gadAB. Analysis of naturally contaminated water and food samples using a gadAB-specific DNA probe that was labeled with digoxigenin showed that a gadAB-based assay is as reliable as standard methods that enumerate E. coli organisms on the basis of lactose fermentation. The presence of few E. coli cells initially seeded into produce rinsates could be detected by PCR to gadA/B genes after overnight enrichment. A multiplex PCR assay using the gadAB primers in combination with primers to Shiga toxin (Stx) genes stx(1) and stx(2) was effective in detecting STEC from the enrichment medium after seeding produce rinsate samples with as few as 2 CFU. The gadAB primers may be multiplexed with primers to other trait virulence markers to specifically identify other pathogenic E. coli groups.

The solution structure of the complex formed between alpha-bungarotoxin and an 18-mer cognate peptide derived from the alpha 1 subunit of the nicotinic acetylcholine receptor from Torpedo californica

The region encompassing residues 181-98 on the alpha1 subunit of the muscle-type nicotinic acetylcholine receptor forms a major determinant for the binding of alpha-neurotoxins. We have prepared an (15)N-enriched 18-amino acid peptide corresponding to the sequence in this region to facilitate structural elucidation by multidimensional NMR. Our aim was to determine the structural basis for the high affinity, stoichiometric complex formed between this cognate peptide and alpha-bungarotoxin, a long alpha-neurotoxin. Resonances in the complex were assigned through heteronuclear and homonuclear NMR experiments, and the resulting interproton distance constraints were used to generate ensemble structures of the complex. Thr(8), Pro(10), Lys(38), Val(39), Val(40), and Pro(69) in alpha-bungarotoxin and Tyr(189), Tyr(190), Thr(191), Cys(192), Asp(195), and Thr(196) in the peptide participate in major intermolecular contacts. A comparison of the free and bound alpha-bungarotoxin structures reveals significant conformational rearrangements in flexible regions of alpha-bungarotoxin, mainly loops I, II, and the C-terminal tail. Furthermore, several of the calculated structures suggest that cation-pi interactions may be involved in binding. The root mean square deviation of the polypeptide backbone in the complex is 2.07 A. This structure provides, to date, the highest resolution description of the contacts between a prototypic alpha-neurotoxin and its cognate recognition sequence.

Expression and spectroscopic analysis of soluble nicotinic acetylcholine receptor fragments derived from the extracellular domain of the alpha-subunit

To facilitate structural studies of the ligand binding region from the nicotinic acetylcholine receptor (nAChR), we have developed methods for the high-level expression and purification of an important functional portion of the N-terminal extracellular domain (ECD) of the alpha-subunit. Two soluble receptor fragments comprising residues 143-210 of the Torpedo californica alpha-subunit were expressed in E. coli: alphaT68His6, which contains a histidine tag, and alphaT68M1, which includes the first transmembrane region, M1, of the alpha-subunit. Both proteins demonstrate saturable, high-affinity alpha-bungarotoxin (Bgtx) binding with an apparent equilibrium KD (3 nM) that is comparable to the affinities reported for preparations comprising the entire alpha-subunit ECD. These results demonstrate that the ECD determinants required for Bgtx recognition of the alpha-subunit are entirely specified by residues 143-210. The binding of small ligands was demonstrated in competition assays with 125I-Bgtx yielding KI values of 58 and 105 microM for d-tubocurarine and nicotine, respectively. Circular dichroism (CD) analysis of monomeric alphaT68His6 protein revealed considerable secondary structure. Furthermore, a cooperative, two-state folding transition was observed upon urea denaturation. To circumvent concentration-dependent aggregation of the alphaT68His6 protein at the millimolar concentrations needed for NMR study, we utilized the M1 transmembrane domain to anchor the recombinant receptor fragment onto membrane-mimicking micelles. Monodispersed preparations of alphaT68M1 in dodecylphosphocholine micelles demonstrate high-affinity Bgtx binding and considerable secondary structure by CD. The structural features revealed in the CD profile appear to undergo a cooperative, two-state folding transition upon thermal denaturation. Initial NMR studies suggest that micellar preparations of the alphaT68M1 fragment are amenable to further high-resolution heteronuclear NMR analysis.

Analysis of bottled water for Escherichia coli and total coliforms

U.S. Food and Drug Administration regulations governing bottled water include microbiological quality guidelines based on coliform counts. Recently, a new MF medium for simultaneous detection of total coliforms and Escherichia coli was developed. This medium, m-ColiBlue24 (m-CB) was compared to m-Endo medium and an International Organization for Standardization standard coliform medium, lactose agar with Tergitol 7. Coliform analysis was conducted on 104 brands of bottled water from 10 countries. Some samples were additionally analyzed for heterotrophic plate count on Pseudomonas sp. populations, including P. aeruginosa. Presumptive coliform colonies were found in 5.8% of the samples with m-CB, 1.9% with m-Endo and 11.5% with lactose agar with Tergitol 7. None of the presumptive coliforms from any of the three media were verified as true coliforms in subsequent analysis. Consequently, the presumptive recovery rates actually represented false-positive error (FPE) rates. The FPE for m-CB and m-Endo were not statistically different (P < 0.05) but the FPE for lactose agar with Tergitol 7 was significantly larger.

A new membrane filtration medium for simultaneous detection and enumeration of Escherichia coli and total coliforms

Recovery of total coliforms and Escherichia coli on a new membrane filtration (MF) medium was evaluated with 25 water samples from seven states. Testing of the new medium, m-ColiBlue24 broth, was conducted according to a U.S. Environmental Protection Agency protocol. For comparison, this same protocol was used to measure recovery of total coliforms and E. coli with two standard MF media, m-Endo broth and mTEC broth. E. coli recovery on the new medium was also compared to recovery on nutrient agar supplemented with 4-methylumbelliferyl-beta-D-glucuronide. Comparison of specificity, sensitivity, false positive error, undetected target error, and overall agreement indicated E. coli recovery on m-ColiBlue24 was superior to recovery on mTEC for all five parameters. Recovery of total coliforms on the new medium was comparable to recovery on m-Endo.

Relationship of membrane phospholipid composition, lactosylceramide molecular species, and the specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase to the molecular species composition of GM3 ganglioside

The ceramide molecular species specificity of rat brain neuron CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase (LacCer alpha 2,3-ST) was determined using 19 molecular species of lactosylceramide incorporated into liposomes prepared with purified rat brain phospholipids. The neuron enzyme displayed a distinct molecular species specificity (which was different than the specificity of liver LacCer alpha 2,3-ST) based on both the long-chain base and the fatty acid composition of the lactosylceramide. Specifically, compared to the liver enzyme, relatively high activities were obtained with d18:1-16:0, d18:1-22:1, and d18:0-18:0 lactosylceramide molecular species. When the lipid composition of the neuron microsomal membranes was altered to resemble that of rat liver Golgi membrane lipids, the activities towards d18:1-16:0, d18:1-22:1, and d18:0-18:0 lactosylceramide molecular species were significantly (P < 0.01) reduced and the molecular species specificity of the neuron enzyme resembled that of liver LacCer alpha 2,3-ST. In the reciprocal experiment in which the lipid composition of the rat liver Golgi membranes was altered to resemble neuron microsomal membrane lipids, the molecular species specificity of liver LacCer alpha 2,3-ST was virtually identical to the specificity obtained with the native neuron enzyme. Analysis of the molecular species composition of lactosylceramide and GM3 in rat liver Golgi membranes revealed that the molecular species composition of rat liver Golgi membrane GM3 was precisely what would be expected based on the molecular species specificity of LacCer alpha 2,3-ST and the molecular species composition of lactosylceramide in the Golgi membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Golgi membrane phospholipid composition on the molecular species of GM3 gangliosides synthesized by rat liver sialyltransferase

Previous studies have demonstrated that there is a change in the molecular species specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase (LacCer alpha 2,3-ST) when the lipid composition of the Golgi membrane is altered (Kadowaki, Grant, and Williams, 1993. J. Lipid Res. 34: 905-914). To understand the basis of this phenomenon, the molecular species specificity of rat liver LacCer alpha 2,3-ST was determined under conditions in which the phospholipid class composition of the Golgi membrane was changed to resemble that of cultured mouse neuroblastoma NB2a cells, a cell line in which LacCer alpha 2,3-ST exhibits no molecular species specificity. The change in the lipid composition of the Golgi membrane was accomplished by incubating the Golgi membrane vesicles with nonspecific lipid transfer protein and a 10-fold excess of liposomes prepared with various proportions of purified rat liver lipids. The molecular species specificity of LacCer alpha 2,3-ST was also determined under conditions where the phospholipid molecular species composition but not the phospholipid class composition of the Golgi membrane was changed, and in which both the phospholipid class and molecular species compositions were changed by using liposomes prepared with lipids purified from a mouse brain tumor (ependymoblastoma). When using liposomes prepared with rat liver lipids, a change in the phospholipid class composition of the Golgi membrane to a composition similar to that of NB2a cells increased rather than decreased the molecular species specificity of rat liver LacCer alpha 2,3-ST.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation of defined molecular species of lactosylceramide by chemical deacylation and reacylation with N-succinimidyl fatty acid esters

A procedure for the preparation of specific molecular species of D-erythro-lactosylceramide involving deacylation and reacylation of lactosylceramide prepared from bovine brain gangliosides is described. Lactosylceramide was N-deacylated by alkaline hydrolysis and the resulting four lysolactosylceramides, which contained d18:1, d20:1, d18:0 and d20:0 long-chain bases, were simultaneously re-N-acylated with the N-succinimidyl ester of either 16:0, 18:0, 20:0, 22:0, 24:0, 20:1, 22:1 or 24:1 fatty acid. The resulting lactosylceramide contained four molecular species of lactosylceramides, i.e., d18:1, d20:1, d18:0 and d20:0 long-chain bases coupled with the fatty acid that was introduced. Lactosylceramides prepared in this manner were separated into four individual molecular species by high-performance liquid chromatography (HPLC). Each of the purified molecular species of lactosylceramide was quantitated by HPLC after derivatization with benzoylchloride and was characterized by mass spectrometry. The yields of reacylated lactosylceramide were 38-58% relative to the starting lactosylceramide; the purity of each of the molecular species of lactosylceramide was greater than 95%.

Mechanism of GM3 ganglioside synthesis. Kinetic study of rat liver CMP-N-neuraminate:lactosylceramide alpha 2,3-sialyltransferase employing 19 molecular species of lactosylceramide

The apparent Km and Vmax of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase (LacCer-alpha 2,3-ST) for lactosylceramide and CMP-N-acetylneuraminic acid were determined using 19 molecular species of lactosylceramide. The Km for lactosylceramide varied 6-fold among these molecular species of lactosylceramide, but there was a poor correlation between the Km for a particular molecular species and the activity of Lac-Cer alpha 2,3-ST for that molecular species. The Km for CMP-N-acetylneuraminic acid also varied depending on the molecular species of lactosylceramide used as substrate, and there was a good correlation between the Km of Lac-Cer alpha 2,3-ST for CMP-N-acetylneuraminic acid and the activity of the enzyme. Kinetic studies indicate that the reaction mechanism of LacCer alpha 2,3-ST is a sequential, Ordered Bi Bi system. From considerations of the effects of the structure of the lactosylceramide molecular species on the Vmax and Km for CMP-N-acetylneuraminic acid, it is likely that LacCer alpha 2,3-ST first binds lactosylceramide and then CMP-N-acetylneuraminic acid and that the rate-limiting step in the reaction is the release of the product GM3.

Effect of membrane lipids on the lactosylceramide molecular species specificity of CMP-N-acetylneuraminate:lactosylceramide sialyltransferase

It has previously been shown that when the molecular species specificity of rat liver Golgi CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase was determined, using as the substrate lactosylceramide (LacCer) incorporated into liposomes prepared with rat liver Golgi lipids, the enzyme showed a pronounced variation in activity towards the various molecular species of LacCer (J. Lipid Res. 1989. 30: 1789-1797). In this paper, -the LacCer molecular species specificity of sialyltransferase from neuroblastoma NB2a cells was examined using five naturally occurring and three synthetic molecular species of LacCer. The enzyme activity was determined by following the formation of [14C]GM3 from CMP-[14C]neuraminic acid and individual molecular species of LacCer incorporated into liposomes. Nonspecific lipid transfer protein was included in the enzyme assay to facilitate the transfer of LacCer and other lipids between the liposomes and the membrane where sialyltransferase is located. In these enzyme assays the liposomes contained approximately 10 times more lipid phosphorus than either the microsomal fraction of NB2a cells or the Golgi fraction of rat liver. Thus, in the presence of nonspecific lipid transfer protein, the lipid composition of the membrane where sialyltransferase is located was modified to resemble the lipid composition of the liposomes. When the molecular species specificity of NB2a cell sialyltransferase was determined with LacCer incorporated into liposomes prepared with NB2a cell lipids, the enzyme showed no specificity towards the various molecular species of LacCer. However, when the molecular species specificity of NB2a cell sialyltransferase was determined with LacCer incorporated into liposomes prepared with rat liver Golgi lipids, the enzyme showed a variation in activity towards the various LacCer molecular species similar to that observed with the liver Golgi enzyme using liposomes prepared with liver Golgi lipids. Likewise, when the molecular species specificity of rat liver Golgi sialyltransferase was determined with LacCer incorporated into liposomes prepared with NB2a cell lipids, the liver enzyme then showed no specificity towards the various molecular species of LacCer. These results indicate that the lipid environment of the membrane can alter the molecular species specificity of sialyltransferase towards its lipid substrate, LacCer.

Effects of pH and Water Activity on Microbiological Stability of Salad Dressing

The water activity and pH of an experimental starch-based salad dressing were varied to evaluate inhibitory effects on microorganisms selected from groups known to be principal dressing spoilage agents. Dressing samples were inoculated with Lactobacillus fructivorans , Zygosaccharomyces bailii , or a yeast isolated from a spoiled commercial salad dressing. Both yeast and L. fructivorans displayed a minimum growth pH of approximately 3.55 to 3.60. The minimum a_w observed was 0.89 for yeast growth and 0.91 for L. fructivorans . Combinations of a_w and pH which imparted microbial stability without use of preservatives are described.

Overnight accommodations for visitors and outpatients: a nationwide study

With the trend toward greater emphasis on ambulatory care and preadmission testing and the need to minimize travel and lodging costs for visitors and outpatients, a closer look at the hospital's role in arranging overnight accommodations becomes necessary. Unfortunately, little literature is available concerning the different types of overnight accommodations arranged by hospitals. The hospital interested in information on how it might upgrade its services to visitors and outpatients must rely primarily on brief descriptions of individual situations such as hospital-owned hotels or hostels and Ronald McDonald Houses. Although the literature indicates that some hospitals do offer some types of overnight accommodation services, the array of arrangements available and the level of hospital involvement is not always clear. Given this lack of information, the staff of the Patient and Visitor Participation Project of the University of Michigan Hospitals decided to conduct a nationwide study.

A dissimilatory nitrite reductase in Paracoccus halodenitrificans

Paracoccus halodenitrificans produced a membrane-associated nitrite reductase. Spectrophotometric analysis showed it to be associated with a cd-cytochrome and located on the inner side of the cytoplasmic membrane. When supplied with nitrite, membrane preparations produced nitrous oxide and nitric oxide in different ratios depending on the electron donor employed. The nitrite reductase was maximally active at relatively low concentrations of sodium chloride and remained attached to the membranes at 100 mM sodium chloride.

Nitrogen oxide reduction in Wolinella succinogenes and Campylobacter species

Wolinella succinogenes cells and extracts reduced nitric oxide, and cells, but not extracts, reduced nitrous oxide. Formate-reduced W. succinogenes extracts generated the 573-nm peak in difference spectra seen previously in response to nitric oxide in denitrifiers. The type strains of several Campylobacter species did not reduce either gaseous oxide. Cells, but not extracts, of C. fetus subspecies (fetus and venerealis) reduced nitrous oxide; acetylene inhibited reduction. Neither cells nor extracts reduced nitric oxide.

Influence of Acetylene on Growth of Sulfate-Respiring Bacteria

At a concentration of 20% of the atmosphere of the culture flasks, acetylene inhibited growth and carbon dioxide production by Desulfovibrio desulfuricans and Desulfovibrio gigas. The bacteria did not reduce acetylene to ethylene, and neither acetylene dicarboxylic acid nor ethylene was inhibitory. At 10%, acetylene was partially inhibitory for the desulfovibrios. At 5%, acetylene impeded the rate but did not limit the extent of growth and catabolism of the desulfovibrios. Desulfotomaculum ruminis was affected only negligibly, if at all, by acetylene and ethylene at any of these concentrations.

Bacterial metabolism under conditions representing pesticide disposal pits

Bacterial cultures were incubated with pesticides at concentrations ranging from 1 to 5,000 ppm. The species selected are important in one or more of the following biogeochemical processes: nitrogen fixation, nitrification, denitrification, sulfur oxidation, sulfate reduction, carbon dioxide fixation, and respiratory carbon dioxide evolution. The pesticides used were atrazine, alachlor, carbaryl, parathion, trifluralin, and 2,4-D. Bacterial cultures were exposed to commercial formulations of these pesticides and to pesticide samples from active disposal pits.

Single arterial trunk arising from the aortic arch

A 59-year-old male with a single, arterial trunk arising from the aortic arch is reported. No orther cases of this anomaly have been confirmed; a review of the literature does not reveal another reported case of this abnormal arterial configuration.

Medium for the selective isolation of members of the genus Pseudomonas from natural habitats

A new medium was developed that was superior to four others tested in selecting for members of the genus Pseudomonas.

A study of the nature of the immediate precursor of the extracellular -amylase of Bacillus amyloliquefaciens. A reappraisal

1. A defined medium was devised for use in washed-cell experiments with post-exponential-phase cultures of Bacillus amyloliquefaciens. The medium allowed alpha-amylase to be secreted, bacterial concentration to increase and l-[U-(14)C]valine to be incorporated into protein at a linear rate, which was the same as in a post-exponential-phase culture, for up to 6h. 2. Determination of the specific radioactivity of l-[U-(14)C]valine in the medium, the intracellular amino acid pool, the cellular protein and the isolated alpha-amylase, after a 3h incubation of washed cells in the defined medium, showed that at least 76% of the alpha-amylase secreted was synthesized de novo. 3. By isolating the alpha-amylase formed during a 6h incubation in the presence of l-[U-(14)C]valine it was shown that the specific radioactivity of the N-terminal valine, within the limits of experimental error, was the same as that of the total valine residues from the complete alpha-amylase molecule. 4. A consideration of these results in relation to the whole literature on the subject strongly supports the idea that there is no reason to suppose that extracellular alpha-amylase is formed from a high-molecular-weight precursor in B. amyloliquefaciens and closely related organisms with identical characteristics of exoenzyme secretion.

Uptake of tritium-labelled testosterone by rat femur: effect of disuse and age

Male rats 1 or 2 months of age at the beginning of the experiment were used. In each animal one leg was immobilized and the contralateral leg was used as control. Immobilization was maintained for 1, 2, or 3 weeks in each age group. Uptake of 3H-testosterone was measured in both femurs of each animal. Uptake of tritiated hormone decreased with age. Immobilization increased hormone uptake. The effect of immobilization on uptake varied with age. Variation in hormone uptake is proposed as an explanation of previously observed reversal of the effect of testosterone upon osteopenia of disuse in rats in these same age groups.