Calf Brain Research Articles

Purification of a novel eIF-2α protein kinase from calf brain

A new eukaryotic initiation factor 2 kinase has been purified for the first time from calf brain cytosol. The purification of a nonabundant novel protein kinase activity, designated as PKI, that phosphorylates the α subunit of eukaryotic initiation factor 2 is described. The protein kinase activity was assayed using purified initiation factor 2 as a substrate and was purified by ammonium sulphate precipitation, conventional chromatography in heparin-Sepharose and phosphocellulose and by high performance size exclusion and anion exchange chromatographies. The protein kinase activity elutes in the region of 140,000 in the size exclusion chromatography and is associated with two different polypeptides a and b, with relative molecular masses of 38,000 and 20,000 and an approximate ratio of 2.5–3.0:1. The protein kinase does not phosphorylate casein or histones and it is independent of cyclic nucleotides. It can be classified as a serine kinase since the phosphorylation of the α subunit of eIF-2 is produced in serine residues. Under these conditions none of the kinase subunits are phosphorylated.

Direct activation of GTP-binding regulatory proteins (G-proteins) by substance P and compound 48/80

The neuropeptide substance P and the polyamine compound 48 80 , both known to activate mast cell secretory processes, increased the rate of GTP γS binding to G-proteins purified from calf brain (G o/G i mixture). The GTPase activity of G-proteins was also increased by substance P and compound 48 80 in a dose-dependent and Mg 2+-dependent way. These effects were similar to those of the wasp venom peptide rnastoparan, another histamine releaser of rat peritoneal and human skin mast cells. This suggests that the secretory property of compound 48 80 and substance P is not due to a receptor-mediated process but, like mastoparan, results from a direct activation of G-proteins.

The isolation and characterization of inositol polyphosphate 4-phosphatase.

We previously identified an alternative pathway for the metabolism of inositol 1,3,4-trisphosphate (Ins(1,3,4)P3) in calf brain. The enzyme responsible for the degradation of Ins(1,3,4)P3 was designated as inositol polyphosphate 4-phosphatase (Bansal, V. S., Inhorn, R. C., and Majerus, P. W. (1987) J. Biol. Chem. 262, 9644-9647). We have now purified this enzyme 3390-fold from calf brain-soluble fraction. The isolated enzyme has an apparent molecular mass of 110 kDa as determined by gel filtration. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the enzyme migrates as a protein of 105 kDa, suggesting that it is monomeric. Among various 4-phosphate-containing inositol polyphosphates, the enzyme hydrolyzes only Ins(1,3,4)P3 and inositol 3,4-bisphosphate (Ins(3,4)P2), yielding inositol 1,3-bisphosphate and inositol 3-phosphate as products. The inositol polyphosphate 4-phosphatase has apparent Km values of 40 and 25 microM for Ins(1,3,4)P3 and Ins(3,4)P2, respectively. The maximum velocities for these two substrates are 15-20 mumol of product/min/mg protein. Ins(1,3,4)P3 is a competitive inhibitor of Ins(3,4)P2 hydrolysis with an apparent Ki of 27 microM implying that the same active site is involved in hydrolysis of both substrates. The final enzyme preparation retained a small inositol polyphosphate 3-phosphatase activity (less than 2% of rate of inositol polyphosphate 4-phosphatase activity) which most likely reflects a contaminant. The enzyme displays maximum activity between pH 6.5 and 7.5. It is not inhibited by Li+, Ca2+, or Mg2+ except at 10 mM divalent ions. Mn2+ inhibits enzyme at high concentrations IC50 = 1.5 mM.

Neuropil vacuolation in brain: a reproducible histological processing artefact

Vacuolation, affecting principally white matter, in animal brains submitted for diagnostic histopathology was attributed to prolonged holding of fixed tissue in 70 per cent alcohol within an enclosed system automatic tissue processor. The effect was consistently reproduced in calf brains but not in pig brains, suggesting a possible species difference in tissue susceptibility. Also, the degree of vacuolation depended on undetermined processor factors additional to prolonged immersion in 70 per cent alcohol. The artefact resembles forms of intramyelinic oedema and can be avoided by holding tissue in primary fixative.

Brain cytochrome oxidase: purification, antibody production, and immunohistochemical/histochemical correlations in the CNS

Cytochrome oxidase (CO) is a mitochondrial energy-generating enzyme used in brain studies as a marker of neural functional activity. The activity of CO in different brain regions, revealed histochemically, is distributed nonhomogeneously but in distinct patterns. Localized differences in CO activity could arise from localized differences in enzyme amount or from localized regulation of enzyme turnover number (molecular activity). To distinguish between these alternatives, we used antibodies against purified calf brain CO to assess the immunohistochemical distribution of CO amount (protein immunoreactivity) in several brain regions. Calf brain mitochondria (synaptic and nonsynaptic populations) were isolated from gray matter homogenates by differential centrifugation. CO was purified from detergent extracts of the mitochondria by cytochrome c-Sepharose 4B affinity chromatography. Antisera against the purified CO were raised in rabbits. The antibodies reacted specifically with CO, predominantly subunit IV, in SDS immunoblots. The antibodies did not react in SDS immunoblots with any other proteins solubilized from mitochondria or caudate nucleus but did cross-react with brain CO from other mammalian species and with bovine heart CO. The immunohistochemical distribution of CO amount matched the histochemical distribution of CO activity in all regions tested, including the monkey hippocampus and the mouse olfactory bulb, somatosensory (barrel) cortex, and cerebellum. Thus, the amount of CO in neural tissue is distributed in the same nonhomogeneous pattern as the histochemical activity of CO. The results suggest that mechanisms exist by which CO molecules are selectively distributed within neurons to meet local metabolic demands posed by neural functional activity.

Identification of dynamin, a novel mechanochemical enzyme that mediates interactions between microtubules

We report that calf brain microtubules prepared without nucleotide contain, in addition to kinesin and dynein, a polypeptide of 100 kd that could be dissociated by nucleotide. The protein was selectively extracted from microtubules using a combination of GTP and AMP-PNP. The extract contained microtubule-stimulated (6-fold) MgATPase activity that partitioned into two components upon further purification: the 100 kd polypeptide and a soluble activating fraction. The 100 kd protein induced microtubules to form hexagonally packed bundles containing periodic cross bridges spaced 13 nm apart. In the presence of ATP and the activating fraction, bundles fragmented, elongated, and exhibited other behavior indicative of sliding between microtubules. These findings indicate that the 100 kd protein is part of a novel mechano-chemical enzyme, which we term “dynamin”, that may mediate microtubule sliding in vivo.

A thermodynamic study of the interaction of tubulin with colchicine site ligands

The bicyclic colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC) has been used to study the thermodynamics of specific ligand binding to the colchicine site of tubulin, employing isothermal reaction microcalorimetry. The binding of MTC to purified calf brain tubulin, in 10 mM sodium phosphate buffer, pH 7.0, is characterized by delta H degree = -19 +/- 1 kJ.mol-1, delta G degree = -31.8 +/- 0.6 kJ.mol-1, and delta S degree = 43 +/- 5 J.mol-1.K-1 at 298 K, with a slight variation in the temperature range from 283 to 308 K. The binding thermodynamics of colchicine and allocolchicine are similar to MTC under the conditions examined, suggesting related molecular interactions of the three ligands with the protein binding site. The standard enthalpy changes of binding of colchicine and MTC at 308 K coincide within experimental error. Therefore the more favorable free energy change of binding of colchicine must come from a larger binding entropy change (by about 20 J.mol-1.K-1). This difference could be attributed to the presence of the middle ring of colchicine, which is absent in MTC. Consistently, a similar entropy change is observed by the comparison of allocolchicine to MTC binding at several temperatures. In addition, allocolchicine binding is about 6 kJ.mol-1 less exothermic than MTC binding, which could be attributed to the presence in allocolchicine of a substituted phenyl ring instead of the colchicine-MTC tropolone ring. The present results and analysis are fully compatible with the previously proposed bifunctional binding of colchicine and MTC (through their trimethoxybenzene and tropolone moieties) to a bifocal protein binding site, and also with a partial immobilization of intramolecular rotation of MTC upon binding, which in colchicine is already constrained by its middle ring (Andreu, J. M., Gorbunoff, M. J., Lee, J. C., and Timasheff, S. (1984) Biochemistry 23, 1742-1752).

Studies on protein methyltransferase in human cerebrospinal fluid

Protein methyltransferases, rich in most mammalian brains, were studied in human cerebrospinal fluid (CSF). Among several well-characterized groups of methyltransferases, protein methylase I (S-adenosylmethionine:protein-arginine N-methyltransferase, EC 2.1.1.23) was found in significant amounts in human CSF samples. Both myelin basic protein (MBP) -specific and histone-specific protein methylase I activities were observed, the latter being generally higher in most CSF. S-Adenosyl-L-homocysteine, a potent product inhibitor for the methyltransferase, inhibited approximately 90% of MBP-specific protein methylase I activity at a concentration of 1 mM. The optimum pH of the MBP-specific protein methylase I was found to be around 7.2. Identity of exogenously added MBP as the methylated substrate for CSF enzyme was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. An amino acid analysis of the [methyl-3H]protein hydrolysate showed two major radioactive peaks cochromatographing with monomethyl- and dimethyl (symmetric)-arginine. Human CSF contained relatively high endogenous protein methylase I activity (activity measured without added substrate protein): The endogenous substrate can be immunoprecipitated by antibody raised against calf brain MBP. Finally, CSF from several neurological patients were analyzed for protein methylase I, and the results are presented.

Dopamine D1 receptors of the calf parathyroid gland: identification of a ligand binding subunit with lower apparent molecular weight but similar primary structure to neuronal D1 receptors

The ligand binding subunit of the calf parathyroid D1 dopamine receptor was visualized by autoradiography following photoaffinity labeling with (+/-)-7-[125I]iodo-8-hydroxy-3-methyl-1-(4'-azidophenyl)-2,3,4,5- tetrahydro-1H-benzazepine ([125I]IMAB) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein comprising the D1 binding subunit migrated with an apparent Mr approximately equal to 62,000. Photoincorporation of [125I]IMAB into the Mr approximately equal to 62,000 polypeptide required the presence of protease inhibitors and was stereoselectively antagonized by dopaminergic agonists and antagonists with an appropriate pharmacological specificity for D1 receptors. The electrophoretic mobility of the [125I]IMAB-labeled receptor was not altered by the absence or presence of urea or thiol-reducing/oxidizing reagents. The Mr approximately equal to 62,000 protein representing the ligand binding subunit of bovine parathyroid D1 receptors corresponds to one of three D1 receptor binding subunits (Mr = 74,000, 62,000, and 51,000) identified in bovine brain. Peptide map comparisons of radiolabeled D1 receptors from calf parathyroid and brain following limited proteolytic digestion with Staphylococcus aureus V8 and papain revealed marked structural similarities. These data suggest that, despite tissue-specific differences in overall molecular weight, both parathyroid and neuronal D1 dopamine binding subunits appear to be pharmacologically and structurally homologous and that the molecular mechanism(s) responsible for the apparent lack of a one to one correspondence in the subunit composition of the D1 receptor in these tissues probably reflect(s) tissue-specific posttranslational modifications.

Differential binding properties of the peripheral-type benzodiazepine ligands [3H]PK 11195 and [3H]Ro 5-4864 in trout and mouse brain membranes.

High-affinity binding sites for [3H]PK 11195 have been detected in brain membranes of rainbow trout (Salmo gairdneri) and mouse forebrain, where the densities of receptors were 1,030 and 445 fmol/mg of protein, respectively. Ro 5-4864 (4'-chlorodiazepam) was 2,200-fold less potent as a competitor of [3H]PK 11195 binding in the piscine than the murine membranes. Investigation of the regional distribution of these sites in trout yielded a rank order of density of spinal cord greater than olfactory bulb = optic tectum = rhombencephalon greater than cerebellum greater than telencephalon. This site in trout shared some of the characteristics of the peripheral-type benzodiazepine receptor (PTBR) (also known as the mitochondrial benzodiazepine receptor) in rodents, i.e., high affinity for PK 11195 and the endogenous ligand protoporphyrin IX, but was unique in the low affinity of Ro 5-4864 (41 microM) and diazepam and the relatively high affinity of the calcium channel ligand diltiazem and two central benzodiazepine ligands, CGS 8216 and CGS 9896. The differential affinity for the two prototypic PTBR ligands in trout is similar to that previously observed in calf and human brain membranes. Structural differences for the trout sites are indicated by the relative inability of diethyl pyrocarbonate to modify histidine residues of the binding site in trout as compared with mouse membranes. Heterogeneity of binding of the two prototypic PTBR ligands in mouse brain membranes was indicated by additivity studies, equilibrium competition experiments, and saturation isotherms, which together support the hypothesis that Ro 5-4864 discriminates between two [3H]PK 11195 binding sites having high (nanomolar) and low (micromolar) affinity, respectively.

Characterization of an imidazoline/guanidinium receptive site distinct from the α2-adrenergic receptor

alpha 2-Adrenergic receptors recognize a number of molecules with diverse chemical structures, including the yohimban diastereoisomers yohimbine and rauwolscine, catecholamines, guanidinium analogs, and imidazolines, such as clonidine. The affinity of the receptor protein for some of these ligands can vary by 10-100-fold among various tissues and species, suggesting a heterogeneous class of binding sites. Certain cellular effects elicited by the compounds possessing an imidazoline or guanidinium moiety may actually be mediated by a membrane receptor distinct from the alpha 2-adrenergic receptor. To determine whether this imidazoline/guanidinium receptive site (IGRS) and the alpha 2-adrenergic receptor represent distinct proteins, we solubilized and partially characterized the two binding sites in rabbit kidney. This tissue expresses both alpha 2-adrenergic receptors and high affinity imidazoline/guanidinium binding sites, the latter which are rauwolscine-insensitive but can be identified with the benzodioxan [3H]idazoxan. The IGRS and alpha 2-adrenergic receptor in rabbit kidney exhibit distinct ligand recognition properties, which are maintained after solubilization and partial purification. In addition, the two receptors can be physically separated by heparin-agarose or lectin affinity chromatography indicating that the two binding sites are distinct entities. [3H]Idazoxan binding is trypsin-sensitive, indicating that the IGRS is a protein rather than a lipid component of the plasma membrane. [3H]Idazoxan binding is not inhibited by endogenous agonists for known neurotransmitter receptors. However, the IGRS does recognize clonidine-displacing substance, a small non-catechol compound isolated from calf brain, suggesting the existence of a previously uncharacterized hormonal/neurotransmitter receptor system.

Protein kinase C catalyzed phosphorylation of sterol carrier protein 2.

The transport of cholesterol to the inner mitochondrial membrane, a key step in steroidogenesis, is subject to hormonal modulation that, at least in part, could be mediated by protein phosphorylation. This step is stimulated by sterol carrier protein 2 (SCP2) and Ca2+. To explore whether SCP2 itself is a potential control point for regulation by Ca2+-dependent phosphorylation we investigated whether highly purified SCP2 could serve as a substrate for major type Ca2+ and non-Ca2+-dependent protein kinases. Phosphorylation by calmodulin protein kinase II (CaM-PK II), myosin light chain kinase (MLCK), cAMP-dependent kinase (PKA) and protein kinase C (PKC) was monitored under optimal conditions for each enzyme. PKA, CaM-PK II and MLCK catalyzed the radiolabeling of histone 2A, synapsin I and myosin light chain (MLC), known substrates for these kinases, respectively, yet no phosphate transfer to SCP2 was observed. In contrast, PKC from two different sources (rat and calf brain) effectively catalyzed the phosphorylation of the highly purified SCP2. The phosphorylation of SCP2 depended on the addition of Ca2+ and phospholipids and was completely blocked by Polymyxin B, a PKC inhibitor. PKC catalyzed phosphorylation of SCP2 displayed a similar dependence on the concentration of ATP. Lineweaver Burk plots of the data indicate Km values for ATP of approximately 6 microM for the phosphorylation of SCP2. Our results, which have revealed for the first time that SCP2 is a substrate for PKC, are consistent with the possibilities that the control of steroidogenesis by tropic hormones and by PKC activation are mediated, at least in part, by the phosphorylation/dephosphorylation of SCP2.

Endocrine responses to 5-hydroxytryptamine-1A receptor activation by ipsapirone in humans

Based on radioligand binding studies, multiple recognition sites for 5-hydroxytryptamine (N-IT) located on neurons within the mammalian central nervous system have been classified as 5HTr and 5-HT2 (Perota 5-I-ITm sites are in extrapyramidal structures of the rat and mouse brain; 5-HT,b receptors are in the brain of calf, pig, and humans (where 5-HTm sites appear to be absent); and 5-HTlc sites are primarily in the choroid plexus (for review, see Tricklebank 1987). Although there is abundant evidence that serotonergic neuronal pathways exert a stimulatory effect on cortisol, prolactin (PRL), and, to a lesser extent, on growth hormone (GH) in humans, the 5-HT receptor subtype mediating the

Identification of the clathrin assembly protein AP180 in crude calf brain extracts by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis

We present a two-dimensional gel electrophoretic method which affords a diagnostic means for the identification of the neuron-specific clathrin assembly protein AP180 in crude cytosolic and microsomal fractions of bovine brain. The method is based on the finding that in the presence of sodium dodecyl sulfate (SDS) in a newly developed continuous high salt Tris-acetate-EDTA buffer system protein AP180 migrates at a rate corresponding to its molecular weight of ‖120,000, while in other more commonly used SDS-polyacrylamide gel electrophoresis methods it behaves anomalously as a 170- to 180-kDa polypeptide. By combining electrophoresis in the Tris-acetate-EDTA system in the first dimension with either the electrophoretic system of Laemmli [Laemmli, U. K. (1970) Nature (London) 227, 680–685] or that of Neville [Neville, D. M. (1971) J. Biol. Chem. 246, 6328–6334] in the second dimension, it is possible to identify AP180 in complex protein mixtures, because it is the only major protein that fell significantly off a diagonal defined by other proteins. A comparison of the microsomal and soluble fractions examined in this manner reveals that most of the AP180 is present in the soluble fraction.

A synchrotron X-ray scattering characterization of purified tubulin and of its expansion induced by mild detergent binding.

This report presents a synchrotron radiation X-ray scattering characterization of calf brain tubulin purified by the modified Weisenberg procedure. The results show that under nonassembly conditions (i.e., in 10 mM sodium phosphate and 0.1 mM GTP, pH 7, buffer) these preparations consist of a uniform population of molecules with a radius of gyration of 3.1 +/- 0.1 nm, which can be interpreted as arising from the native alpha-beta heterodimer. The uniformity in the population persists even at unusually high concentrations of protein. Binding of colchicine or substitution of GTP by GDP does not induce, within the statistical accuracy and resolution range of our measurements, any significant structural modification in soluble tubulin. In assembly buffer [i.e., 10 mM sodium phosphate, 6 mM magnesium chloride, 1 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, 1 mM GTP, and 3.4 M glycerol, pH 6.5], these preparations readily assemble into microtubules upon increasing the temperature from 4 to 37 degrees C. Binding of nondenaturing amphiphiles to soluble tubulin provides a simplified model for tubulin-membrane interactions. The X-ray scattering data show that the radius of gyration of tubulin progressively increases upon binding of the mild detergent sodium deoxycholate, reaching a maximum value of 4.3 +/- 0.1 nm at detergent saturation. The relative increase in the radius of gyration coincides within experimental error with the previously determined relative increase in the frictional coefficient [Andreu, J.M., & Muñoz, J.A. (1986) Biochemistry 25, 5220-5230]. Analysis of these observations suggests that the effect of detergent binding is to induce an isotropic swelling of the protein structure.

Phenylazoxycyanide damages microtubular protein more than its reference antibiotic, calvatic acid

The effect of phenylazoxycyanide and calvatic acid, its reference antibiotic, on some functions of tubulin obtained from different sources has been studied. Our purpose was to establish a possible correlation between the antitumour activity of these drugs and their antimicrotubular action. Microtubules are subcellular structures involved in proliferation and maintenance of the cell shape and probably in malignant transformation; indeed most antimitotic drugs influence the stability of microtubules through the interaction with tubulin, their main protein. In this work we found phenylazoxycyanide impairs, more than calvatic acid, polymerization of purified tubulin from calf brain. It also damages, in a dose-dependent manner, colchicine-binding ability of tubulin derived from rat liver and AH-130 Yoshida ascite hepatoma cells. Compounds displaying an azoxycyano group may represent new antimicrotubular agents and their effect could be modulated by the different polarity and structural characteristic of the molecule.

28 kDa adenosine-binding proteins of brain and other tissues.

Membranes prepared from calf brain were solubilized and chromatographed on a column containing 5'-amino-5'-deoxyadenosine covalently linked to agarose through the 5'-amino group. When the column was eluted with adenosine, a pure protein emerged with subunit molecular mass of 28 kDa. The protein was extracted from the membranes with sodium cholate, but not with 100 microM-adenosine or 0.5 M-NaCl. A similar 28 kDa protein was isolated from the soluble fraction of calf brain. The yield of membrane-bound and soluble 28 kDa protein per gram of tissue was about the same. The 28 kDa protein was also found in membrane and soluble fractions of rabbit heart, rat liver and vascular smooth muscle from calf aorta. The yield per gram of tissue fell into the order brain greater than heart approximately vascular smooth muscle greater than liver for the 28 kDa protein from the membrane fraction, and brain approximately heart greater than vascular smooth muscle greater than liver for the 28 kDa protein from the soluble fraction. Polyclonal antibodies to pure 28 kDa protein from calf brain membranes cross-reacted with the 28 kDa protein from calf brain soluble fraction and with 28 kDa proteins isolated from other tissues. The 28 kDa protein from calf brain membranes was also eluted from the affinity column by AMP and 2',5'-dideoxyadenosine, but at a concentration higher than that at which adenosine eluted the protein, but N6-(R-phenylisopropyl)adenosine, 5'-N-ethylcarboxamidoadenosine, ADP, ATP, GTP, NAD+, cyclic AMP and inosine failed to elute the protein at concentrations up to 1 mM. The 28 kDa protein from the soluble fraction was not eluted by 3 mM-AMP or 1 mM-N6-(R-phenylisopropyl)adenosine,-5'-N-ethylcarboxamidoadenosine or -cyclic AMP. Unexpectedly, the soluble 28 kDa protein was eluted by AMP in the presence of sodium cholate. Soluble 28 kDa protein from calf brain had a KD for adenosine of 12 microM. Membrane 28 kDa protein from calf brain had a KD of 14 microM in the presence of 0.1% sodium cholate. Amino acid compositions of the 28 kDa proteins were similar, but not identical.

Photolabeled tryptic degradation products of benzodiazepine-binding proteins are glycopeptides Implications for localization of cleavage sites

Crude synaptic membranes of avian and mammalian brain tissue were photolabeled with the benzodiazepine-receptor ligand [ 3H]flunitrazepam and subsequently treated extensively with trypsin followed by incubation with endoglycosidase F. SDS-polyacrylamide gel electrophoresis and fluorography revealed that the final tryptic degradation product of 25 kDa in both pigeon and calf brain is deglycosylated in two steps. These results were confirmed by immunoblots of similarly pretreated membranes of pig brain using the α-subunit-specific monoclonal antibody bd-24. Benzodiazepine-receptor binding and its enhancement by GABA are largely retained after trypsinization. Based on the proposed transmembrane topology for the α-subunits of the GABA/benzodiazepine receptor, we suggest that the large N-terminal domain of benzodiazepine-binding proteins is protected against tryptic cleavage.

Amphomycin Inhibits Mannosylphosphoryldolichol Synthesis by Forming a Complex with Dolichylmonophosphate

The inhibitory effect of the lipopeptide antibiotic amphomycin on the mechanism of mannosylphosphoryldolichol biosynthesis by calf brain rough endoplasmic reticulum membranes has been studied extensively. Calf brain rough endoplasmic reticulum membranes when incubated with varying concentrations of GDP-mannose in the presence and absence of amphomycin showed no significant difference in apparent Km for GDP-mannose (1.08 and 1.37 microM, respectively). However, the Vmax was reduced to 0.17 pmol/mg protein/min in the presence of amphomycin as compared with 1.86 pmol/mg protein/min in its absence. On the other hand, when mannosylphosphoryldolichol synthase activity was measured in the presence of amphomycin and as a function of dolichylmonophosphate (Dol-P) concentrations, the shape of the substrate velocity curve changed from a rectangular hyperbola to a sigmoid. The Hill coefficients (n) for this reaction were calculated to be 2.02 and 1.22 in the presence and absence of the antibiotic and the corresponding Km values for Dol-P were found to be 333 and 47.3 microM, respectively. In separate experiments when radiolabeled antibiotic was reacted with Dol-P in the presence of Ca2+, a complex was formed. The complex formation was dependent on both Ca2+ in the reaction mixture and fatty acid residue on the antibiotic. Similar complex formation was also observed with undecaprenylmonophosphate. No such complex, however, was formed with dolichylpyrophosphate, with undecaprenylpyrophosphate, or with their free alcohols (dolichol or undecaprenol). Furthermore, when an equimolar mixture of Dol-P and phosphatidylserine was reacted with the antibiotic under identical conditions, the complex formation was observed selectively with Dol-P. These data demonstrated that amphomycin interacted with the active site of the glycosyl-carrier lipid (Dol-P), thereby preventing its participation at the enzymatic reaction.

31P NMR studies of excised gray and white calf brain

1. 1. 31P NMR examination of isolated calf gray and white matter reveals that white matter contains higher levels of the phosphodiester glycerolphosphoryl choline (GPC) than gray. 2. 2. It is suggested that GPC may play a role in maintaining the level of phospholipids present by inhibition of phospholipases. 3. 3. The spectra also reveal a skewed peak whose maximum is at −11 ppm which is inferred to arise from myelin-like structures. 4. 4. The results show that phosphorus spectra from the brain must be carefully considered whether they arise from the same type tissue or represent a mixed sample since variation in results may represent anatomy as well as physiology.