Altered sympathetic tone in hypertensives with angina and lowered threshold for pacing ischemia

To determine the role of the sympathetic nervous system in myocardial ischemia with essential hypertension, plasma norepinephrine, heart rate (HR), blood pressure (BP), and the HR.BP double product at the time of silent ischemia during pacing and exercise treadmill test (ETT) were compared with basal values in 20 patients with sustained essential hypertension and stable angina, 3 to 60 days (12.6 +/- 11.6) after discontinuation of all antihypertensive and coronary vasodilator therapy. Group I (N = 6) had silent ischemia with a higher HR.BP product at ETT than at pacing (ratio = 157 +/- 10.4% [+/- SD] v a value in group II [N = 5] of 102 +/- 18.8 [P less than .01]. Group III (N = 9) had no silent ischemia at ETT or pacing. Group I v group II plasma norepinephrine levels at rest and with pacing silent ischemia were 76 +/- 37 v 138 +/- 36 pg/mL, P less than .02, and 101 +/- 50 v 230 +/- 43 pg/mL, P less than .01, respectively. In groups I and II plasma norepinephrine levels were significantly lower than those of group III. Eleven of 20 patients had ischemia on pacing or ETT. Left ventricular myocardial mass were greater (224 +/- 49 v 180 +/- 28 g, p less than .05), HR (67 +/- 13 v 76 +/- 11 beats/min, P = NS) and plasma norepinephrine levels at rest (104 +/- 47 v 241 +/- 99 pg/mL, P less than .01), pacing (160 +/- 81 v 338 +/- 94 pg/mL, P less than .01), and ETT (758 +/- 268 v 1203 +/- 611 pg/mL, P less than .05), were lower in patients with ischemia (N = 11, group II) than in patients without ischemia (N = 9, group III) on pacing or ETT. Eight patients were on reserpine prestudy; reserpine prestudy was associated with lower basal HR (63 +/- 9 v 76 +/- 12 beats/min, P less than .05) and plasma norepinephrine (106 +/- 48 v 169 +/- pg/mL, P less than .07) and greater ratio of HR.BP double product on ETT/pacing, (141 +/- 33 v 111 +/- 19, P less than .02). The sympathetic nervous tone of group I was low at baseline but there may have been raised alpha/beta-receptor responsiveness to laboratory stresses with concomitant micro/macrovascular constriction at higher oxygen demand.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood pressure reactivity and sympathetic hyperactivity. Predictors of hypertension

Raised sympathetic nerve activity appears to be a predictor and factor in primary hypertension. Sympathetic activation alone does not appear to be a sufficient cause of sustained hypertension, however. Over the past two decades we have studied several populations of primary hypertensive patients and found neural hyperactivity in 25 to 30% of them. Metaanalyses of other studies have supported these findings.

The effect of substrate composition and condition on resorption by isolated osteoclasts

Osteoclasts isolated from 10-day-old rabbits were studied in a cell culture system to obtain further insight into the possible mechanisms involved in the process of bone resorption. Osteoclasts were cultured on the surfaces of devitalized mammalian bones, a composite of polycrystalline synthetic hydroxyapatite and geological single crystal hydroxyapatite. The structural interaction of osteoclasts with these various substrates was morphologically characterized by using a scanning electron microscope. Viable osteoclasts were observed to adhere and extend pseudopodia and filopodia for all cases of calcium-phosphate surfaces. However, actual resorbing process was only observed in devitalized bone surfaces. Resorption pits of various sizes were found in multiple series and showed a preference for mineral-exposed area over collagen-exposed area. The difference observed between resorption of those areas of bone surface and the failure of osteoclasts to resorb non-tissue substrates are discussed in relation to current theories of the mechanisms of mineral dissolution and resorption in mammalian calcified tissues.

Lattice fringe studies of (100) defects in enamel crystallites

Lattice imperfections in the structure of shark (Nataprion brevirostrais) enamel crystallites have been studied by means of lattice-imaging in a high-resolution transmission electron microscope. Line defects exhibiting various lengths (100-2500 A) and widths (10-30 A) and demonstrating phase behaviour different from that of the host crystal were observed along the fringes representing (100) lattice planes. When defect sites were subjected to an electron beam, an annealing process was observed in which the difference in phase contrast eventually disappeared and the defect itself became an intricate part of the (100)-type lattice planes. A through-focal series of the defects show a reversal in phase contrast. By examining the contrast behaviour under certain focal conditions and by adopting the Fresnel diffraction mode, the refractive index of the defect regions was determined to be lower than that of the apatite crystal. Present findings suggest that the interlayering structure along the (100) planes is responsible for the line defects observed in enamel apatites.

Plasma norepinephrine in Chagas' cardioneuromyopathy: a marker of progressive dysautonomia

Chronic Chagas' disease produces pathologic changes of the cardiovascular, digestive, and autonomic nervous systems. In an attempt to elucidate the nature of the dysautonomia in patients with Chagas' disease, we measured plasma norepinephrine levels, blood pressure, and heart rate, both supine and standing in 26 patients, and compared these values of patients classified according to three clinical subsets of cardiovascular manifestations with the values of nine normal volunteers and 16 patients with nonchagasic heart failure. Results suggested (1) progressive blockade of the alpha receptor in patients with Chagas' disease who have minimal clinical symptoms (group I) and in those who have ECG alterations without congestive symptoms (group II), as reflected by normal or raised plasma norepinephrine levels without change of diastolic blood pressure during standing, which indicates absent postural reflexes; and (2) blockade associated with partial denervation in patients with Chagas' disease who have class III or IV heart failure (group III), as suggested by a lower supine plasma norepinephrine level and a fall in diastolic blood pressure in the upright position. The findings of reduced plasma norepinephrine levels are in contrast to the elevated plasma norepinephrine levels in patients without Chagas' disease with class III and IV heart failure who have sympathetic hyperactivity.

Noradrenergic activity and silent ischaemia in hypertensive patients with stable angina: effect of metoprolol

30 patients (10 normotensive, 20 hypertensive) with stable angina and positive treadmill exercise tests entered a double-blind, placebo-controlled crossover trial of metoprolol, 100 mg twice daily. At the end of each treatment phase, blood pressure was monitored for 24 h and Holter and real-time electrocardiographic (ECG) monitoring were carried out and an activity diary kept for 48 h. Blood samples for catecholamine measurement were taken after 30 min supine, 60 min standing, and at the first silent ischaemic event, triggered by the real-time ECG monitor, by means of an ambulatory blood withdrawal pump. Metoprolol lowered blood pressure and heart rate in both normotensive and hypertensive subjects, and reduced the frequency and duration of silent ischaemic episodes in hypertensive subjects. Plasma noradrenaline measured during silent ischaemia while the patients were resting was significantly higher than the control supine level without ischaemia. These findings suggest that noradrenergic hyperactivity may have a role in coronary vasoconstriction and that treatment which neutralizes sympathetic tone may be especially beneficial in treatment of silent ischaemia in hypertensive patients.

The three-dimensional spatial relationship between the collagen fibrils and the inorganic calcium-phosphate crystals of pickerel and herring fish bone

High-voltage (1.0 mega-volt) electron stereomicroscopy has been used to examine the spatial relationship between the inorganic crystals and the collagen fibrils of pickerel and herring bone. Stereomicrographs of cross sections of the collagen fibrils encompassing regions of initial to full mineralization showed that the calcium phosphate crystals are located within the collagen fibrils. In all stages of mineralization, calcium-phosphate deposits were not observed associated or within membrane-bound structures. Serial cross sections of the fully mineralized collagen fibrils were three-dimensionally reconstructed using the computer graphic imaging process. Findings from this study suggest that there exist a local "bulging" along the fibrils corresponding to the 680 A periodicity in which additional mass of minerals were observed to be accommodated within the collagen fibril structure at this sites.

Use of cultured embryonic chicken osteoblasts as a model of cellular differentiation and bone mineralization

When chicken embryonic progenitor cells were selected and grown in culture as previously described, by 30 days cellular differentiation could be demonstrated by expression of in vivo levels of osteocalcin, alkaline phosphatase (APase), type I collagen and phosphoproteins (PP). Ultrastructural analysis revealed that the cultures were similar morphologically to young osteoid in vivo with structural features including well-developed, orthogonally arranged collagen fibrils with 64-70 nm periodicity and electron opaque areas consisting of very poorly crystalline hydroxyapatite. Analysis of collagen synthesis versus collagen accumulation in the matrix indicated a temporal inconsistency between the time of synthesis and accumulation, suggesting that accumulation was largely controlled at the level of fibril formation. Analysis of PP accumulation demonstrated a 10-fold increase in total phosphoamino acid content over the 30 day time course. PP synthesis analyzed by [3H]-Ser(P) and [14C]-Thr(P) incorporation showed an induction similar to that seen for APase. Experiments undertaken to characterize the nature of PP synthesized by the cultures identified a unique 66 kD protein. This protein was purified from chick tibial and calvarial bone and a polyclonal antibody was raised in rabbits. Ultrastructural immunocytochemistry using this antibody and the protein A-gold technique revealed specific immunolabelling over regions of mineralizing matrix in vitro, a reaction identical to that observed for the distribution of this 66 kD PP in vivo during embryonic tibial bone development in the chicken.

Effects of celiprolol on plasma renin, aldosterone, norepinephrine and epinephrine in primary hypertension

Celiprolol is a newly developed cardioselective beta-blocking agent with mild beta 2-agonist and weak alpha 2-antagonist properties. To evaluate the acute (2.5 hours) and chronic (2 weeks) effects of celiprolol (400 mg once a day) on plasma renin, aldosterone, norepinephrine and epinephrine, 20 patients with mild to moderate primary hypertension were studied in a double-blind placebo-controlled crossover trial. Two and one-half hours after the first dose of both placebo and celiprolol, supine and standing measurements of blood pressure showed a significant reduction, whereas plasma norepinephrine increases were comparable with baseline values. Placebo and celiprolol produced similar changes on supine blood pressure and plasma norepinephrine. In 9 patients celiprolol decreased plasma renin (from a mean +/- standard deviation of 1.09 +/- 0.35 to 0.77 +/- 0.52 ng/ml/hr, p less than 0.05) and aldosterone (from 9.2 +/- 3.7 to 6.7 +/- 3.9 ng/dl, p less than 0.05) acutely both supine and standing, but placebo did not change these parameters. Celiprolol increased pulse rate supine (but not standing) as compared with baseline values. After 2 weeks of celiprolol therapy, blood pressure was decreased both supine and standing compared with placebo in 18 patients (140 +/- 18/88 +/- 8 vs 149 +/- 18/94 +/- 7, 136 +/- 18/91 +/- 6 vs 142 +/- 20/97 +/- 9 mm Hg, respectively, each p less than 0.05), without a change of pulse rate when supine and with a reduction when standing. There were no significant changes of plasma renin, aldosterone, norepinephrine and epinephrine levels during chronic therapy compared with placebo.

Behavioral vs beta-blocker therapy in patients with primary hypertension: effects on blood pressure, left ventricular function and mass, and the pressor surge of social stress anger

We compared the relative effects of relaxation therapy, conventional hygienic techniques, and a beta-receptor blocker, atenolol, on control of arterial pressure, left ventricular mass, and diastolic function in patients with mild primary hypertension. Furthermore, we related these effects to baseline neural tone and its changes and assessed the efficacy of relaxation or the pressor surge of "social stress" anger. In group I left ventricular mass index was related to both systolic and diastolic blood pressure (r = 0.46; p less than 0.05). Plasma norepinephrine was related to age (r = 0.33; p less than 0.01). Slope was inversely related to both plasma norepinephrine (r = -0.29; p less than 0.05) and age (r = -0.31; p less than 0.05). Relaxation therapy reduced both supine systolic and diastolic blood pressures, 4.5% and 7.6%, respectively, but did not affect plasma norepinephrine. Hygienic informational therapy reduced plasma norepinephrine by 18%, (p less than 0.05) and did not change blood pressure. Blood pressure responders to nondrug therapy (i.e., diastolic blood pressure reduction of 7% or more) had a 7% reduction of left ventricular mass index (p less than 0.02). On the other hand, atenolol reduced systolic and diastolic blood pressure by 10% and 15%, respectively, (p less than 0.01) and improved left ventricular function by 17% (p less than 0.05) without a significant change in left ventricular mass index. Finally, relaxation therapy but not hygienic therapy reduced systolic blood pressures 4% and 6%, respectively (p less than 0.01), both before and during social stress anger.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen expression, ultrastructural assembly, and mineralization in cultures of chicken embryo osteoblasts

A newly defined chick calvariae osteoblast culture system that undergoes a temporal sequence of differentiation of the osteoblast phenotype with subsequent mineralization (Gerstenfeld, L. C., S. Chipman, J. Glowacki, and J. B. Lian. 1987. Dev. Biol. 122:49-60) has been examined for the regulation of collagen synthesis, ultrastructural organization of collagen fibrils, and extracellular matrix mineralization. Collagen gene expression, protein synthesis, processing, and accumulation were studied in this system over a 30-d period. Steady state mRNA levels for pro alpha 1(I) and pro alpha 2 collagen and total collagen synthesis increased 1.2- and 1.8-fold, respectively, between days 3 and 12. Thereafter, total collagen synthesis decreased 10-fold while mRNA levels decreased 2.5-fold. In contrast to the decreasing protein synthesis after day 12, total accumulated collagen in the cell layers increased sixfold from day 12 to 30. Examination of the kinetics of procollagen processing demonstrated that there was a sixfold increase in the rate of procollagen conversion to alpha chains from days 3 to 30 and the newly synthesized collagen was more efficiently incorporated into the extracellular matrix at later culture times. The macrostructural assembly of collagen and its relationship to culture mineralization were also examined. High voltage electron microscopy demonstrated that culture cell layers were three to four cells thick. Each cell layer was associated with a layer of well developed collagen fibrils orthogonally arranged with respect to adjacent layers. Fibrils had distinct 64-70-nm periodicity typical of type I collagen. Electron opaque areas found principally associated with the deepest layers of the fibrils consisted of calcium and phosphorus determined by electron probe microanalysis and were identified by electron diffraction as a very poorly crystalline hydroxyapatite mineral phase. These data demonstrate for the first time that cultured osteoblasts are capable of assembling their collagen fibrils into a bone-specific macrostructure which mineralizes in a manner similar to that characterized in vivo. Further, this matrix maturation may influence the processing kinetics of the collagen molecule.

Labetalol blunts morning pressor surge in systolic hypertension

Twenty-four-hour ambulatory blood pressure, including the acceleration phase, and left ventricular mass were evaluated in 16 patients with isolated systolic hypertension (standing blood pressure greater than or equal to 160 mm Hg systolic and less than or equal to 95 mm Hg diastolic). After a 4-week, single-blind, placebo period, each patient underwent 24-hour ambulatory blood pressure monitoring and echocardiography. Labetalol therapy was then initiated at 100 mg twice a day in a single-blind manner and increased weekly by 100 mg twice a day until blood pressure control was obtained or a maximum dosage of 400 mg twice a day was reached. Blood pressure control was achieved at a mean daily dose of 363 +/- 46 mg of labetalol. Measurements were repeated at the end of an 8-week maintenance phase. Labetalol therapy significantly reduced the mean 24-hour systolic ambulatory blood pressure from 154 +/- 8 (mean +/- SEM) mm Hg at baseline to 142 +/- 6 mm Hg (p greater than 0.01) and controlled the early morning surge in systolic ambulatory blood pressure. Minor reductions in diastolic blood pressure and heart rate were statistically but not clinically significant. Left ventricular mass was not changed. Labetalol monotherapy provides effective 24-hour control of systolic blood pressure, including the acceleration phase, in patients with isolated systolic hypertension.

Noradrenergic hyperactivity in primary hypertension; central and peripheral markers of both behavioral pathogenesis and efficacy of sympatholytic and relaxation therapy

The effects of clonidine or relaxation therapy were determined in two separate groups of patients with primary hypertension. Ten patients were treated with clonidine monotherapy for 3 months. There were concurrent reductions of blood pressure, plasma and CSF norepinephrine, all p less than 0.01. The changes of blood pressure and norepinephrine were correlated, p less than 0.05 and 0.01, respectively. Thirty patients received hygienic instructions, and 17 of them had relaxation training in addition. Relaxation lowered blood pressures, p less than 0.01, the reduction of blood pressure was related to baseline plasma norepinephrine, p less than 0.05, and greater in patients with "raised" plasma norepinephrine, p less than 0.02. Plasma norepinephrine was lowered after hygienic therapy, p less than 0.05, the change was not significant after relaxation training. Arterial pressure elevation appears to be related to raised plasma norepinephrine. This noradrenergic hyperactivity is a marker for blood pressure responsiveness to sympatholytic therapy with clonidine or relaxation techniques.

Neurohumoral mechanisms and left ventricular hypertrophy: effects of hygienic therapy

To determine the effects of hygienic (non-drug) therapy on blood pressure (BP) control and its relationship to sympathetic tone and left ventricular mass (LVM) in primary hypertension, plasma norepinephrine (NE) and renin activity (PRA), LVM, and nutritional and behavioral status were assessed in 76 borderline to mild hypertensives. Pretherapy plasma NE was related to diastolic blood pressure (DBP) and PRA (r = 0.24, P less than .05 and r = 0.37, P less than .01, respectively). Plasma NE of high renin patients (221 +/- 52) (mean +/- SD) was greater than that of normal renin patients (159 +/- 61, ng/l, P less than .01). LVM was related to systolic blood pressure (SBP) (P less than .001), DBP (P less than .01) and urinary sodium (P less than .05), and inversely related to PRA (P less than .01). Septal wall thickness was related to hostility (r = 0.42, P less than .05). After seven weeks of hygienic therapy, DBP was reduced by 6 mmHg (P less than .01). The change in SBP was related to baseline plasma NE (P less than .05) and inversely related to LVM (P less than .05). These results suggest that raised sympathetic tone may be a pathogenic factor in primary hypertension and that hygienic therapy lowers BP more effectively in patients with raised sympathetic tone and low LVM.

Unusual case of an ectopic spleen

A rare case of a very unusual position of a normally functioning spleen in the posterior aspect of the right lobe of the liver is reported. A 6-year-old boy was evaluated with echocardiography for congenital heart disease of coexisting atrial and ventricular septal defects with pulmonary hypertension. Other associated cardiac abnormalities on this child included a right-sided aortic arch, drainage of the azygous vein into the superior vena cava and an Eisenmenger complex. At the time of echocardiography, absence of the spleen in its normal location was noted. This prompted further investigation into localizing the spleen using 99mTc-sulfur colloid and heat denatured 99mTc-RBC scintigraphy. Both scans demonstrated the spleen to lie posterior to the right hepatic lobe.

Cervical myelopathy attributable to pseudogout. Case report with radiologic, histologic, and crystallographic observations

A 77-year-old woman complained of numbness in her hands and feet, progressive unsteadiness, weakness, and loss of proprioception of six months' duration. A myelogram revealed stenosis of the spinal canal at the levels of C2-3, T6-7, L2-3, and L3-4. On computerized tomography scan, a large dorsal, epidural, soft tissue mass and focal calcification of the ligamentum flavum were seen at C3. Laboratory studies ruled out gout, collagen disease, vitamin B12 deficiency, syphilis, parathyroid, and thyroid disease. At decompressive laminectomy, a nodular mass in the ligamentum flavum (C2-4) was found and removed. Three months after operation, the neurologic symptoms had improved. Histologic examination of the elastic ligament revealed deposits of birefringent crystals, which were identified by X-ray diffraction as calcium pyrophosphate dihydrate (CCPD). Only about six cases of myelopathy attributable to deposits of CPPD appear to have been previously reported.

The solid, calcium-phosphate mineral phases in embryonic chick bone characterized by high-voltage electron diffraction

The solid mineral phases of calcium-phosphate (Ca-P) in the long bones from embryonic chicks between the ages of 9 and 13 days have been examined by high voltage (1.0 MV) electron microscopy and electron microdiffraction. The study was undertaken to identify the chemical and crystallographic nature of the inorganic mineral phase(s) prepared under conditions which significantly reduce artifacts of specimen preparation and microscopic examination of the tissues. Electron microdiffraction patterns of solid mineral phase particles in the osteoid matrices of the subperiosteal region of tibiae were principally those of poorly crystalline hydroxyapatite. In rare instances (less than 1% of the estimated volume of the mineral phase present in the zone of early mineralization), relatively large single crystals were observed within clusters of hydroxyapatite. From calculations of both interplanar spacings and measurements of angular displacement of diffraction reflections from single crystal microdiffraction patterns, two distinct phases other than hydroxyapatite were identified: brushite and beta-tricalcium phosphate. A third phase, resembling an apatite, remains unidentified. The results suggest that very small amounts of nonapatitic phases of Ca-P exist in chicken bone tissue. No temporal relationship could be established between the nonapatitic and apatitic phases. There is at present no evidence from this study to support the concept that nonapatitic phases are precursors of a final apatitic phase in bone.

Detection and localization of silicon and associated elements in vertebrate bone tissue by imaging ion microscopy

The growing long bones from normal embryonic chicks and young rats have been examined in situ by imaging ion microscopy, a highly sensitive technique for elemental detection and localization. In tibial diaphyses from chick and rat, treated with anhydrous ethylene glycol, embedded in Spurr medium, and dry sectioned 1-2 microns thick, analyses revealed the presence of silicon, calcium, magnesium, carbon, and oxygen. Silicon localization was principally extracellular in the tissues. Comparison of single element maps of silicon and calcium indicated that silicon specifically appeared in putative uncalcified osteoid regions of tibiae. Detection and imaging of silicon by ion microscopy support results of earlier work by Carlisle, who demonstrated the element in osteoid of rat and mouse bone by electron probe microanalysis. The current data offer the possibility for characterizing more completely silicon interaction in vertebrate calcified tissues.

Microbeam electron diffraction and lattice fringe studies of defect structures in enamel apatites

A microbeam diffraction method in transmission electron microscopy has been applied to lattice structural studies of human and shark enamel apatite crystals. The technique allows diffraction patterns to be obtained from very small regions of the specimen (40 nm in diameter) and transfers minimal energy to the sample during analysis. The presence of crystal defects, nonisolated dislocations with the dislocation line positioned perpendicular to the 100-type planes, was observed in the central part of the crystals. Further experiments with acid-etching of crystals containing such defects showed an initial preferential dissolution at the site of these atomic imperfections. The relative abundance of the crystal defects was approximately the same in both human enamel and shark enameloid.

Yeast adhesion in the pathogenesis of endocarditis due to Candida albicans: studies with adherence-negative mutants

Two spontaneous cerulenin-resistant mutants of Candida albicans, 4918-2 and 4918-10, were unable to adhere in vitro in fibrin-platelet clots. Because in vitro adherence correlates well with colonization of nonbacterial thrombotic endocarditis on traumatized valvular endocardium, 50% infectious dose studies were performed with a rabbit model of endocarditis. Wild-type C. albicans required 10(3.6) +/- 0.12 cfu in comparison with 10(5.73) +/- 0.31 and 10(7.3) +/- 0.21 cfu for mutants 4918-2 and 4918-10, respectively. The relative avirulence of mutant strains in producing endocarditis was not attributed to accelerated clearance of these strains from the bloodstream. In fact, clearance of wild-type and mutant strains was almost identical. In the same animals renal candidiasis was observed with all strains of C. albicans, although the number of cfu per gram of kidney was higher after infection with wild-type C. albicans. Thus, strains of C. albicans with reduced ability to adhere in vitro to a fibrin-platelet matrix are relatively avirulent in the rabbit endocarditis model.

In vitro concatemerization of bacteriophage T7 DNA: role of DNA synthesis and gene 6 exonuclease

The replication of bacteriophage T7 DNA in vivo proceeds via the synthesis of complex concatemeric intermediates which are joined via the 160 base pair terminal redundancies at either end of the phage chromosome. To gain some insight into the mode of generation of these structures, we have examined the role of DNA synthesis in the formation of concatemeric bacteriophage T7 DNA in vitro. Incubation of mature T7 DNA with T7-infected cell extracts and a deoxynucleoside [32P]triphosphate resulted in the incorporation of significant radioactivity into the DNA. Highest levels of incorporation were at the termini of the DNA and decreased toward the middle of the molecule. Incorporation was dependent upon the presence of the activity of the gene 6 exonuclease and correlated with the generation of concatemeric DNA. A model explaining the role of exonucleolytic degradation and DNA synthesis in the generation of concatemeric DNA is presented.

Some physico-chemical properties of deciduous enamel of children with and without pre-natal fluoride supplementation (PNF)

Physico-chemical investigations of enamel from deciduous teeth of a small number of children with and without pre-natal fluoride supplementation (PNF) exhibited the following differences between the PNF and non-PNF enamel, with the former showing: (a) more homogeneous and less extensive patterns of acid-etching; (b) denser crystal populations in intra-prismatic regions; (c) larger prism dimensions; (d) greater total mineral density (wt%ash); (e) higher degree of crystallinity; (f) smaller a-axis dimensions; and (g) more fluoride and less carbonate contents. On the basis of these preliminary findings, further studies with larger numbers of samples would seem appropriate.

Bacteriophage T7 defective in the gene 6 exonuclease promotes site-specific cleavages of T7 DNA in vivo and in vitro

Site-specific cleavages of intracellular DNA were demonstrated in bacteriophage T7 6am-infected cells. The sites of the cleavages were located at 46.8 and 68.7% (1% of the T7 DNA length = 400 base pairs) from the left end of the T7 genome. These cleavages required the products of genes 3 (endonuclease), 4 (DNA primase), and 5 (DNA polymerase). However, the product of gene 6 (exonuclease) must be absent. Site-specific cleavage was also shown to occur in vitro in extracts of T7 6am-infected cells, although at a different site: 82.8% from the left end of the T7 genome.

Effect of pore diffusion limitation on dextrin hydrolysis by immobilized glucoamylase

Data reported here and previously indicate that when dextrin is hydrolyzed in the presence of immobilized glucoamylase, use of a larger average molecular weight substrate leads to lower overall rates of hydrolysis, while the maltose concentration during the bulk of the reaction and the maximum glucose concentration are lower than when the soluble form of the enzyme is employed under the same conditions. Computer simulation of the system demonstrated that all three observations were caused by pore diffusion limitation: the first by slow diffusion of substrate, the second by slow diffusion of intermediates, and the third by slow diffusion of glucose. Follow-up experiments with glucoamylase immobilized to particles of different sizes confirmed this finding, as results with the smallest beads were identical to those with soluble glucoamylase.

Pilot plant production of glucose with glucoamylase immobilized to porous silica

Glucoamylase was immobilized to porous silica and its kinetics and stability were observed with acid- and alpha-amylase-hydrolyzed dextrin as feed. The enzyme was found to be extremely stable in both laboratory and pilot plant operations. When the feed had been previously only lightly hydrolyzed, pore diffusion limitation caused appreciable decreases in glucose production rate. The severity of starch hydrolysis to dextrin markedly affected ultimate glucose yields. The diffusional gradients present in the carrier pores caused the immobilized enzyme to yield lower glucose concentrations than the free enzyme at similar feed conditions.