Fibre in the prevention and management of chronic disease

Some of the evidence of the role of dietary fibre in the prevention and treatment of disease is reviewed and the heterogeneous nature of fibre is considered. The relationships between various fibre fractions and colonic disorders, including cancer, diabetes mellitus, hypercholesterolaemia and obesity are discussed. It is concluded that an increase of dietary fibre constituents is only one part of a programme of dietary modification relevant to chronic diseases of a Western industrialised society.

Alcohol and beer consumption in relation to cancers of bowel and lung: an extended correlation analysis

Some extensions to simple international correlation analyses are examined with reference to beer consumption and bowel and lung cancers in 29 countries. Simple correlation of cross-sectional data for beer consumption and rectal cancer yields a coefficient of 0.77 in males and 0.75 in females. Lagged correlation analyses show a different temporal relationship between beer and colon cancer (little change over time) and rectal cancer (maximal correlation for contemporaneous, i.e. cross-sectional, data sets). Lagged correlation analysis of beer consumption and lung cancer shows a similar pattern to that for rectal cancer and beer, and markedly different from that for lung cancer and cigarettes, the former showing maximal correlation for contemporaneous data, the latter peaking 15 yr prior to date of mortality. Changes in beer consumption over time correlate with subsequent changes in rectal cancer, particularly amongst younger age groups. The sex-ratio of rectal cancer varies from around 1 in low beer consumption countries to about 1.75 in high consumption countries. The utility of these extensions to the usual simple correlation analyses is considered. The biologic plausibility of beer-bowel cancer relationships, and possible mechanisms, are discussed in the light of the findings.

Fluorescence studies of the interaction of calmodulin with myosin light chain kinase

The interaction of calmodulin with myosin light chain kinase produces an approximately 30% increase in myosin light chain kinase tryptophan fluorescence. This represents the first report of calmodulin-induced structural changes in a protein which it activates. We fund that the calmodulin-myosin light chain kinase interaction is: 1) dependent on [Ca2+] (half-maximal binding at pCa 6.2) and essentially independent of [Mg2+], 2) occurs before saturation of all four reported Ca2+-specific sites on calmodulin. 3) saturates with 1 mol of calmodulin bound per mol of kinase with an apparent affinity of approximately 2.0 X 10(7) M-1, 4) is specific for calmodulin over troponin-C, 5) is directly related to the activation of myosin light chain kinase for phosphorylation of myosin light chain. Fluorescence stopped flow studies of these calmodulin-induced fluorescence changes in myosin light chain kinase indicate that Ca2+ binding to calmodulin occurs very rapidly and is not rate-limiting while the calmodulin-induced fluorescence increase in myosin light chain kinase occurs as a biphasic process with rates of approximately 65 s-1 and 6 s-1. The fluorescence increase produced by calmodulin binding to myosin light chain kinase is completely reversed by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid at a rate of approximately 2 s-1.

Studies on phosphorylation of canine cardiac sarcoplasmic reticulum by calmodulin-dependent protein kinase

Two endogenous protein kinase activities, cAMP-dependent and calmodulin-Ca2+-dependent, are associated with isolated cardiac sarcoplasmic reticulum (SR) vesicles. Both kinases phosphorylate an endogenous substrate of approximately 22,000 daltons (phospholamban). The phosphorylation of phospholamban by either the intrinsic or by exogenous cAMP-dependent protein kinase is found to be Ca2+-independent between 0.05 and 100 microM free Ca2+. Calmodulin-dependent phosphorylation, on the other hand, does not require cAMP and is absolutely dependent on the presence of free Ca2+ over a concentration range that corresponds to physiological levels (10(-7) to 10(-5) M). Phosphorylation of SR vesicles by both kinases is additive and the extent of saturation of the cAMP-specific sites has no effect on the degree of stimulation by calmodulin or its Ca2+-dependence. Trifluoperazine, an inhibitor of calmodulin, inhibits calmodulin-dependent phosphorylation without affecting cAMP-dependent phosphorylation, indicating the presence of two types of kinases. This is made further evident by the selectivity of each kinase for exogenous substrates. Whereas cAMP-dependent protein kinase appears to phosphorylate histone ILA (a basic protein) preferentially, calmodulin-dependent protein kinase prefers phosvitin (an acidic protein).

Interaction of calmodulin with skeletal muscle myosin light chain kinase

Studies on myosin light chain kinase isolated from rabbit skeletal muscle show that the enzyme has a molecular weight of 80,000--84,000 with a sedimentation coefficient of 3.2 S and an apparent Stokes radius of 53 A. Gel filtration chromatography with a 3H-labeled calmodulin using a Hummel--Dryer technique shows that the enzyme will bind 1 mol of calmodulin per mol of enzyme, with an affinity of (1.9 +/- 0.5) x 10(7) M-1 in the absence of substrate. The calmodulin dependence of enzyme activation at limiting Mg2+ and light chain concentrations confirms this observation. The calcium dependence of activation of the enzyme--calmodulin complex is characterized by a Hill coefficient of 2.5, with half-activation occurring at 6.6 x 10(-7) M Ca2+. The amino acid composition shows a high percentage (9.1%) of proline, which may account for the large apparent Stokes radius and no clear resemblance to other skeletal muscle proteins. A comparison of the amino acid composition with that from turkey gizzard shows some resemblance.

Magnesium and the regulation of muscle contraction

There are a variety of Ca2+ binding sites in muscle (e.g., troponin, parvalbumin, myosin, and calmodulin) that may play a role in the regulation of muscle contraction an other enzymatic processes. since most of these proteins also bind Mg2+, it is important to consider the effect that the high free Mg2+ concentration (mM) found in muscle has on the Ca2+ binding properties of these sites. The major effect of Mg2+ is to greatly reduce the rate of Ca2+ binding to the sites that bind Mg2+ and Ca2+ competitively (Ca2+-Mg2+-type sites found in troponin, parvalbumin, and myosin, which would be essentially saturated with Mg2+ in a relaxed muscle) due to the slow dissociation of bound Mg2+. Thus during a transient increase in [Ca2+] similar to that which would occur during muscle activation, these sites would bind very little Ca2+ and, consequently, could not play a regulatory role. Even if Ca2+ were able to bind to these sites during muscle activation (e.g., if the free Mg2+ in muscle is lower than presumed), the dissociation of Ca2+ from these sites would be quite slow due to their very slow off rates for Ca2+, again making these sites unsuitable for participating in a rapid Ca2+-induced switching mechanisms. In contrast, the Ca2+-specific-type (regulatory) sites found in troponin and calmodulin do not have these restraints. The rate of Ca2+ binding to these sites is not affected by Mg2+ and the off rate of Ca2+ from these sites is very rapid due to their lower Ca2+ affinity. Thus, these sites are able to respond to rapid Ca2+ transients, an essential feature for any Ca2+ binding site that plays a regulator role.

The time-course of Ca2+ exchange with calmodulin, troponin, parvalbumin, and myosin in response to transient increases in Ca2+

We have modeled the time-course of Ca2+ binding to calmodulin, troponin, parvalbumin, and myosin in response to trains of transient increases in the free myoplasmic calcium ion concentration (pCa). A simple mathematical expression was used to describe each pCa transient, the shape and duration of which is qualitatively similar to those thought to occur in vivo. These calculations assumed that all individual metal binding sites are noninteracting and that Ca2+ bind competitively to the Ca2+-Mg2+ sites of troponin, parvalbumin, and myosin. All the on-and-off rate constants for both Ca2+ and Mg2+ were obtained either from the literature or from our own research. The percent saturation of the Ca2+-Mg2+ sites with Ca2+ was found to change very little in response to each pCa transient in the presence of 2.5 X 10(-3)M Mg2+. Our analysis suggests that the Ca2+ content of these sites is a measure of the intensity and frequency of recent muscle activity because large changes in the Ca2+ occupancy of these sites can occur with repeated stimulation. In contrast, large rapid changes in the amount of Ca2+ bound to the Ca2+-specific sites of troponin and calmodulin are induced by each pCa transient. Thus, only sites of the "Ca2+-specific" type can act as rapid Ca2+-regulatory sites in muscle. Fluctuation in the total amount of Ca2+ bound to these sites in response to various types of pCa transients further suggests that in vivo only about one-half to one-third of the total steady-state myofibrillar Ca2+-binding capacity exchanges Ca2+ during any single transient.

A trial of the effects of soya-bean flour and soya-bean saponins on plasma lipids, faecal bile acids and neutral sterols in hypercholesterolaemic men

1. The hypothesis that soya-bean saponins, by binding bile salts in the gastrointestinal lumen, are responsible for some of the plasma-cholesterol-lowering effect of soya-bean preparations, was tested. In a double-blind crossover study 50 g soya-bean flour/d, containing either 22 or 4 g saponins/kg (adjusted by ethanol extraction) was incorporated in biscuits as a substitute for biscuits or bread into the diet of ten outpatient hypercholesterolaemic men over two consecutive 4-week study periods. The diet was monitored to ensure constancy, saponin-rich foods excluded, faeces collected for bile acid and neutral sterol analysis, and blood taken for plasma lipoprotein lipid analysis. 2. Neither diet had any effect on cholesterol in any plasma lipoprotein fraction, on fasting plasma triglyceride, or on faecal bile acids and neutral sterols. 3. These results suggested that soya-bean saponins are not responsible for the hypocholesterolaemic effect of soya-bean products.

Purification of actin from cardiac muscle

Actin from cardiac acetone and ether powders is compared to actin from skeletal acetone powder using a modification of an established extraction procedure. The yield of actin from cardiac ether powder is nearly the same as the yield from skeletal acetone powder whereas significantly less actin is obtained from cardiac acetone powder. Sodium dodecyl sulfate polyacrylamide gel electrophoresis shows the actins from each of the sources to be virtually identical in terms of purity and mobility. Molecular sieve chromatography of G-actin demonstrates cardiac actin from ether powder to have identical polymerization and mobility properties as skeletal actin from acetone powder. A simplified procedure, developed for highly purified actin from muscle powder and prepared in a single day is presented. The storage of F-actin at -80 degrees C is also discussed.

The calcium and magnesium binding sites on cardiac troponin and their role in the regulation of myofibrillar adenosine triphosphatase

The cardiac troponin (Tn) complex, consisting of a Ca2+-binding subunit (TnC), an inhibitory subunit (TnI), and a tropomyosin-binding subunit (TnT), has been reconstituted from purified troponin subunits isolated from bovine heart muscle. The Ca2+-binding properties of cardiac Tn were determined by equilibrium dialysis using either EGTA or EDTA to regulate the free Ca2+ concentration. Cardiac Tn binds 3 mol Ca2+/mol and contains two Ca2+-binding sites with a binding constant of 3 X 10(8) M-1 and one binding site with a binding constant of 2 X 10(6) M-1. In the presence of 4 mM MgC12, the binding constant of the sites of higher affinity is reduced to 3 X 10(7) M-1, while Ca2+ binding to the site at the lower affinity is unaffected. The two high affinity Ca2+-binding sites of cardiac Tn are analogous to the two Ca2+-Mg2+ sites of skeletal Tn, while the single low affinity site is similar to the two Ca2+-specific sites of skeletal Tn (Potter, J. D., and Gergely, J. (1975) J. Biol. Chem. 250, 4625-5633). The Ca2+-binding properties of the complex of TnC and TnI (1:1 molar ratio) were similar to those of Tn. Cardiac TnC also binds 3 mol of Ca2+/mol and contains two sites with a binding constant of 1 X 10(7) M-1 and a single site with a binding constant of 2 X 10(5) M-1. Assuming competition between Mg2+ and Ca2+ for the high affinity sites of TnC and Tn, the binding constants for Mg2+ were 0.7 and 3.0 X 10(3) M-1, respectively. The Ca2+ dependence of cardiac myofibrillar ATPase activity was similar to that of an actomyosin preparation regulated by the reconstituted troponin complex. Comparison by the Ca2+-binding properties of cardiac Tn and the cardiac myofibrillar ATPase activity as a function of [Ca2+] and at millimolar [Mg2+] suggests that activation of the ATPase occurs over the same range of [Ca2+] where the Ca2+-specific site of cardiac Tn binds Ca2+.

Calcium dependent regulation of brain and cardiac muscle adenylate cyclase

The very close interdependence of Ca2+ and hormones in the overall metabolism of cyclic nucleotides has recently been emphasized by Cheung. Clearly the results presented here show that [Ca2+] in the physiological range (less than 10(-7) M to greater than 10(-6) M) has profound effects on the activity of adenylate cyclase from both brain and cardiac muscle. Whereas both brain and cardiac cyclase exhibit a Ca2+ dependent inhibition (perhaps mediated by calmodulin), only the brain cyclase is activated by Ca2+ via calmodulin. With both cyclases there is an inverse relationship between the inhibition of cyclase and the activation of calmodulin dependent (cAMP and cGMP) phosphodiesterase as a function of Ca2+ concentration. Because the IC50's for Ca2+ are the same in both heart and brain, the possibility exists that the Ca2+ inhibitory site of both cyclases is similar and perhaps identical. Considering the ability of Ca2+ to both stimulate and inhibit cyclase, one could imagine that in different species, tissues, or regions of the same tissue, there could exist multiple populations of cyclase, that is a cyclase which would only show Ca2+ dependent inhibition, Ca2+ dependent stimulation, or the biphasic response to Ca2+ (FIGURE 7). The fact that Ca2+ still regulates adenylate cyclase after various stimuli (histamine, NaF, etc.) suggests that Ca2+ may function to regulate the cyclase over shorter time periods (regardless of its state of stimulation) and that other affectors of cyclase (e.g., hormones) would serve to regulate the cyclase over longer time periods.

A fluorescent probe study of Ca2+ binding to the Ca2+-specific sites of cardiac troponin and troponin C

Cardiac troponin C (C-TnC) was labeled with the sulfhydryl-specific fluorescent probe molecule 2-(4'-iodoacetamidoanilino)naphthalene-6-sulfonic acid at cysteine 35 and 84 to produce C-TnCIA. This modified protein binds Ca2+, undergoes Ca2+-induced increases in alpha helix, and forms a complex with other troponin subunits as does unlabeled C-TnC. C-TnCIA undergoes a small fluorescence decrease with Ca2+ or Mg2+ binding to the two high affinity Ca2+-Mg2+ sites of C-TnC and a large biphasic approximately 2.1-fold fluorescence increase with Ca2+ binding to two lower affinity Ca2+-specific sites with KCa of approximately 4.5 X 10(5) M-1 and approximately 5 X 10(2) M-1. C-TnCIA was formed in a complex with troponin I (TnI) and troponin T to form C-TnIA. This fluorescent reconstituted whole troponin undergoes a 25% decrease with Ca2+ binding to a Ca2+-specific site of KCa approximately 3 X 10(6) M-1. C-TnC, therefore, contains a single Ca2+-specific site of approximate equal affinity as the two Ca2+-specific regulatory sites of skeletal TnC. This Ca2+-specific site in C-TnC (like its two corresponding sites in S-TnC) undergoes an approximate 10-fold increase in affinity in whole troponin or when TnC is complexed with TnI. Since the two Ca2+-specific sites in skeletal troponin have been shown to be the regulatory sites of skeletal muscle contraction we suggest that this single Ca2+-specific site, of equal affinity, in C-TnC is the regulatory site of cardiac muscle contraction.