Calcium ion stimulated endogenous protein kinase catalyzed phosphorylation of peripheral and central nerve myelin proteins: comparison between normal and genetically dystrophic mouse

Myelin isolated from the peripheral (PNS) and central nervous system (CNS) of mouse contained a protein kinase which catalyzed phosphorylation of myelin proteins. In the case of CNS myelin, small and large basic proteins were phosphorylated whereas in the case of PNS myelin, a glycoprotein (Po) as well as other basic proteins (P1 and P2) were phosphorylated. Ca2+, but not adenosine 3',5'-monophosphate (cyclic AMP), markedly (5- to 10-fold) stimulated phosphorylation of PNS and CNS myelin proteins. There was no difference between the normal and dystrophic mouse CNS myelin phosphorylation. However, a marked decrease in the cauda equina PNS myelin phosphorylation ofthe dystrophic mouse was observed. Interestingly, the dystrophic sciatic nerve myelin phosphorylation, compared to normal, was higher.

Calcium ion stimulated endogenous protein kinase catalyzed phosphorylation of peripheral nerve myelin proteins

Myelin isolated from the rat peripheral nervous system (sciatic nerve and cauda equina) contained Mg2+-dependent protein kinase that phosphorylated myelin polypeptides. Ca2+, in micromolar concentrations, markedly stimulated phosphorylation (half-maximal stimulation at 5 microM (free) Ca2+) but at higher concentrations (greater than 100 microM Ca2+) it caused inhibition. In the presence of Triton X-100, phosphorylation (+/-Ca2+) of myelin was increased and Ca2+ caused up to a 10-fold increase in phosphorylation. Among the myelin polypeptides, P0 (Mr, 28 000), a major glycoprotein, accounted for nearly 60% of the total phosphate incorporated into the myelin and Ca2+ markedly promoted phosphorylation of P0. Phosphorylation of other myelin polypeptides, P2 (Mr, 16 000), Y (Mr, 26 000), and P1 (Mr, 20 000), and the Ca2+-stimulatory effect on phosphorylation of these were also evident. Cyclic AMP (or other cyclic nucleotides) failed to show any significant stimulatory effect on myelin phosphorylation.

Glycogen phosphorylase activities in skeletal muscle and heart of genetically dystrophic Syrian hamster

A simple, rapid and reliable procedure of tissue preparation was devised to estimate glycogen phosphorylase activity in cardiac and skeletal muscle of normal and genetically dystrophic Syrian hamsters of various ages. Total phosphorylase activities of dystrophic skeletal muscle, compared to normal, were reduced. Except for the case of heart from the younger dystrophic animals (45 days old), in which higher phosphorylase activity was noted, hearts from dystrophic hamsters, compared to normal, also showed reduced phosphorylase activities. There were, however, no significances in the ratios of phosphorylase alpha to total phosphorylase between the normal and dystrophic tissues.

Regional and subcellular distribution of myocardial muscarinic cholinergic receptors

Regional and subcellular distributions of muscarinic cholinergic receptors were investigated in the myocardium of commonly used laboratory animals. The density of receptor sites (expressed in terms of either pmol/g protein or pmol/g tissue), amongst the regions examined, was found much higher in right and left atrium in the case of rat and rabbit whereas for the guinea pig and dog, the distribution was diffuse. However, irrespective of the species and/or region studies, the microsomal fraction, amongst the subcellular fractions, showed the highest enrichment or receptors.

Protein analysis of cardiac sarcolemma: effects of membrane-perturbing agents on membrane proteins and calcium transport

Protein composition of cardiac sarcolemmal membranes was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Membranes were observed to contain about 20 polypeptide bands ranging from 18000 to 200 000 dalton mass. Out of these, six bands were prominent and together comprised 57% of the membrane protein. When sarcolemmal membranes, phosphorylated by [gamma-(32)P] ATP in the presence of Ca(2+) or Na+ with and without K+, were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis at pH 2.4, the band III region (Mr 105 000) of gels was found to contain active sites of monomeric Ca-ATPase and (Na,K)ATPase. Bands I (Mr greater than 200 000), II (Mr 150 000), III (Mr 105 000), and VI (Mr 47 000) were accesible to trypsin; the extent of proteolysis was dependent on the time of exposure to, and the concentration of, trypsin (i.e, ratio of sarcolemmal protein/trypsin). Addition of molar sucrose protected sarcolemmal proteins from the tryptic proteolysis. Calcium transport was reduced by the action of trypsin; the degree of reduction was influenced by the time of exposure of membranes to trypsin as well as the concentration of trypsin. (Mg,Ca)ATPase activity, on the other hand, was elevated moderately at lower concentration and reduced at higher concentration of trypsin. Treatment with phospholipase C cium transport and (Mg,Ca)ATPase activity; electrophoretic patterns were unaffected by this treatment. Addition of lecithin to phospholipase C treated membranes produced a moderate increase in calcium transport. Exposure to Triton X-100 (1%) specifically solubilized three protein bands (Mr90 000, 67 000, and 57 000), whereas exposure to deoxycholate (1%) preferentially solubilized high-molecular-weight proteins, including band III (Mr 105 000); Lubrol-PX (1%) caused nonspecific solubilization of proteins, although the extent of solubilization with Lubrol-PX was considerably less than with either Triton or deoxycholate.

Differential effects of non-ionic detergents on microsomal and sarcolemmal adenylate cyclase in cardiac muscle

1. About 4 and 23% of the homogenate adenylate cyclase activity was recovered in the microsomal and sarcolemmal fractions isolated from guinea-pig heart ventricles. 2. Cardiac microsomal adenylate cyclase activity [basal as well as p[NH]ppG (guanyl-5'-yl imidodiphosphate)- and NaF-stimulated] was increased over 2-fold in the presence of Lubrol-PX (0.01-0.1%). 3. The sarcolemmal enzyme, however, showed concentration-dependent inhibition caused by the detergent under all assay conditions, except when p[NH]ppG was included in the assay. In the latter case, the detergent (0.01-0.02%) caused a modest increase (30-45%) in enzyme activity. 4. Another non-ionic detergent, Triton X-100, also stimulated the microsomal cyclase and inhibited the sarcolemmal enzyme. 5. With either membrane fraction, Lubrol-PX solubilized the enzyme when the detergent/membrane protein ratio was 2.5 (mumol of detergent/mg of protein). 6. The findings with homogenate and a washed particulate fraction resembled those obtained with sarcolemma, and those with isolated sarcoplasmic reticulum resembled those with microsomal preparations. 7. p[NH]ppG, and to some extent NaF, protected the detergent-induced inactivation of the enzyme observed at higher detergent concentrations (0.5% Lubrol-PX and 0.05-0.5% Triton X-100). 8. In the absence of detergents, p[NH]ppG increased the basal enzyme activity about 2-fold in microsomal fractions, but did not appreciably stimulate the sarcolemmal enzyme. Isoproterenol, on the other hand, increased the sarcolemmal enzyme activity (>2-fold) in the presence of p[NH]ppG and caused only moderate stimulation (31%) of the microsomal enzyme under these conditions. 9. These findings support the view that, although the bulk of adenylate cyclase resides in heart sarcolemma (plasma membrane), the microsomal activity cannot be accounted for solely by contamination of the microsomal fraction with sarcolemma, as has been suggested by others [Besch, Jones & Watanabe (1976) Circ. Res.39, 586-595; Engelhard, Plut & Storm (1976) Biochim. Biophys. Acta451, 48-61]. Further, the results of this study show that cardiac sarcoplasmic-reticulum membranes possess this enzyme.

Stimulation of cardiac sarcolemmal (Na+--K+) ATPase activity by phosphorylase kinase

Following preincubation with phosphorylase kinase, ATPase activities of heart sarcolemmal membranes were increased: total ATPase from 9.38+/-0.65 to 15.25+/-0.90 and ouabain-sensitive (Na+--K+)ATPase from 1.67+/-0.17 to 3.12+/-0.33 micron moles Pi/mg protein/h (mean +/- S.E. of 3 experiments); (Ca2+)ATPase and (Mg2+--Ca2+)-ATPase activities were not significantly altered due to phosphorylase kinase. Under these conditions, phosphorylase kinase catalyzed phosphorylation of sarcolemmal membranes. The kinase-catalyzed phosphorylation of membranes was increased by Ca2+ ions: at pH 6.8, 30% increase in phosphorylation was observed whereas at pH 8.5, 267% increase was noted due to this action. These findings support the view that Ca2+-dependent phosphorylation of membranes regulates (Na+--K+)ATPase.

Stimulation of calcium accumulation in cardiac sarcolemma by phosphorylase kinase

After incubation with phosphorylase kinase, calcium accumulation in cardiac sarcolemma was increased from 65+/-2 to 95+/-3nmol/10min per mg of protein. Under these conditions, phosphorylase kinase catalysed phosphorylation of membranes. This phosphorylation was hydroxylamine-insensitive, was stimulated by Ca2+ ions and was unaffected by 3':5'-cyclic AMP.

Catecholamine-sensitive adenylate cyclase of caudate nucleus and cerebral cortex. Effects of guanine nucleotides

1. GTP and GMP-P(NH)P (guanyl-5'-yl imidodiphosphate) were observed to increase the stimulation of neural adenylate cyclase by dopamine (3,4-dihydroxyphenethylamine) and noradrenaline. 2. GMP-P(NH)P had a biphasic effect on the enzyme activity. 3. Preincubation of membranes with GMP-P(NH)P activated the enzyme by a process dependent on time and temperature. Catecholamines increased the speed and the extent of this activation. 4. Membrane fractions contained high- and low-affinity sites for GMP-P(NH)P binding: this binding was due to protein(s) of the membrane preparations. 5. Low-affinity-site binding of GMP-P(NH)P appeared to be related to the stimulatory effect on the adenylate cyclase activity.

Adenosine triphosphate - dependent calcium binding and accumulation by guinea pig cardiac sarcolemma

Sarcolemma isolated from guinea pig heart ventricles possessed ATP-dependent Ca2+ binding and accumulation (+ oxalate) activities which were not inhibited by sodium azide, oligomycin, or ruthenium red. Ca2+ binding and accumulation by sarcolemma were sensitive to pH, the optimum being about pH 6.8. The concentrations of ATP required for half-maximal binding and accumulation were 94.3 and 172 muM, respectively. Mg2+ up to 5 mM significantly enhanced both activities but was inhibitory at higher concentrations (greater than 10 mM). Sarcolemmal Ca2+ binding and accumulation were stimulated 100% by K+, half-maximal enhancement occurring at 5-10 mM K+. Ca2+ binding and accumulation were both saturable processes and the respective apparent Km values for Ca2+ were 16.4 and 14.3 muM. Ca2+ binding by sarcolemma was a rapid process and the bound Ca2+ was released upon depletion of ATP in the medium. It is suggested that the sarcolemmal Ca2+ transport system may well be of significance in regulation of the contraction-relaxation cycle of cardiac muscle.

Adenylate cyclase, guanylate cyclase and cyclic nucleotide phosphodiesterases of guinea-pig cardiac sarcolemma

1. The activities of the enzymes involved in the metabolism of cyclic nucleotides were studied in sarcolemma prepared front guinea-pig heart ventricle; the enzyme activities reported here were linear under the assay conditions. 2. Adenylate cyclase was maximally activated by 3mM-NaF; NaF increased the Km for ATP (from 0.042 to 0.19 mM) but decreased the Ka for Mg2+ (from 2.33 to 0.9 mM). In the presence of saturating Mg2+ (15 mM), Mn2+ enhanced adenylate cyclase, whereas Co2+ was inhibitory. beta-Adrenergic amines (10-50 muM) stimulated adenylate cyclase (38+/-2%). When added to the assay mixture, guanyl nucleotides (GTP and its analogue, guanylyl imidophosphate) stimulated basal enzyme activity and enhanced the stimulation by isoproterenol. By contrast, preincubation of sarcolemma with guanylyl imidodiphosphate stimulated the formation of an 'activated' form of the enzyme, which did not reveal increased hormonal sensitivity. 3. The guanylate cyclase present in the membranes as well as in the Triton X-100-solubilized extract of membranes exhibited a Ka for Mn 2+ of 0.3 mM; Mn2+ in excess of GTP was required for maximal activity. Solubilized guanylate cyclase was activated by Mg2+ only in the presence of low Mn2+ concentrations; Ca2+ was inhibitory both in the absence and presence of low Mn2+. Acetylcholine as well as carbamolycholine stimulated membrane-bound guanylate cyclase. 4. Cylic nucleotide phosphodiesterase activities of sarcolemma exhibited both high-and low-Km forms with cyclic AMP and with cyclic GMP as substrate. Ca2+ ions increased the Vmax. of the cyclic GMP-dependent enzyme.

Guanylate cyclase. Subcellular distribution in cardiac muscle, skeletal muscle, cerebral cortex and liver

1. Guanylate cyclase of every fraction studied showed an absolute requirement for Mn2+ ions for optimal activity; with Mg2+ or Ca2+ reaction was barely detectable. Triton X-100 stimulated the particulate enzyme much more than the supernatant enzyme and solubilized the particulate-enzyme activity. 2. Substantial amounts of guanylate cyclase were recovered with the washed particulate fractions of cardiac muscle (63-98%), skeletal muscle (77-93%), cerebral cortex (62-88%) and liver (60-75%) of various species. The supernatants of these tissues contained 7-38% of total activities. In frog heart, the bulk of guanylate cyclase was present in the supernatant fluid. 3. Plasma-membrane fractions contained 26, 21, 22 and 40% respectively of the total homogenate guanylate cyclase activities present in skeletal muscle (rabbit), cardiac muscle (guinea pig), liver (rat) and cerebral cortex (rat). In each case, the specific activity of this enzyme in plasma membranes showed a five- to ten-fold enrichment when compared with homogenate specific activity. 4. These results suggest that guanylate cyclase, like adenylate cyclase, and ouabain-sensitive Na+ + K+-dependent ATPase (adenosine triphosphatase), is associated with the surface membranes of cardiac muscle, skeletal muscle, liver and cerebral cortex; however, considerable activities are also present in the supernatant fractions of these tissues which contain very little adenylate cyclase or ouabain-sensitive Na+ + K+-dependent ATPase activities.