Phase slip and current flow in finite samples of charge-density-wave materials.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
S Ramakrishna
Publications and source records attributed to S Ramakrishna.
Advance directives for the elderly: a survey.
In 1991, the New Jersey Legislature passed the New Jersey Advance Directives for Health Care Act. We surveyed the elderly about their knowledge and interest in advance directives, their preferences regarding end-of-life care, and whether their physicians discuss these matters.
Advance Directives↗
Identification of multifunctional ATP-citrate lyase kinase as the alpha-isoform of glycogen synthase kinase-3.
Multifunctional ATP-citrate lyase kinase (ACLK) exhibits several properties that are similar to glycogen-synthase kinase-3 (GSK-3). The molecular cloning of two distinct mammalian GSK-3 cDNAs and a Drosophila melanogaster (fruitfly) homologue, zeste-white3sgg, has established the existence of a GSK-3 subfamily. A multifunctional protein kinase first identified as an ACLK has recently been shown to exhibit several similarities to the alpha- and beta-forms of GSK-3. Here we have used immunological and biochemical analyses to directly compare these enzymes. Thus purified preparations of ACLK isolated from brain and liver preferentially cross-react with anti-GSK-3 alpha antisera and phosphorylate previously defined substrates of GSK-3 at identical sites. Conversely, both alpha- and beta-forms of GSK-3 phosphorylated ATP-citrate lyase at the same site(s) targeted by ACLK. These, and other similarities, demonstrate ACLK to be identical with, or highly related to, GSK-3 alpha, the implications of which are discussed.
Animals↗
Charge-density-wave phase slip and current conversion in NbSe3.
Explore the source record for details and available documents.
Journal Article↗
Phase slip in charge-density-wave systems.
Explore the source record for details and available documents.
Journal Article↗
Theory of charge-density-wave dynamics.
Explore the source record for details and available documents.
Journal Article↗
Sequence of sites on ATP-citrate lyase and phosphatase inhibitor 2 phosphorylated by multifunctional protein kinase (a glycogen synthase kinase 3 like kinase).
Multifunctional protein kinase (MFPK) phosphorylates ATP-citrate lyase on peptide B on two sites, BT and BS, on threonine and serine, respectively, inhibitor 2 on a threonyl residue, and glycogen synthase at sites 2 and 3. The phosphorylation sites BT and BS of ATP-citrate lyase are dependent on prior phosphorylation at site A whereas site A phosphorylation is decreased by prior phosphorylation at sites BT and BS. To study the MFPK recognition sites and the site-site interactions, the amino acid sequences of ATP-citrate lyase peptide B and inhibitor 2 were determined and compared to each other and to glycogen synthase sites 3-5. The sequence of the tryptic peptide containing the two phosphorylation sites of peptide B is -Phe-Leu-Leu-Asn-Ala-Ser-Gly-Ser-Thr-Ser-Thr(P)-Pro-Ala-Pro-Ser(P)-Arg-, and the sequence of the MFPK phosphorylation site of inhibitor 2 is -Ile-Asp-Glu-Pro-Ser-Thr(P)-Pro-Tyr-. This inhibitor 2 site is identical with the site phosphorylated by glycogen synthase kinase 3/FA. These results suggest that at least some of the sites phosphorylated by MFPK (BT of ATP-citrate lyase, Thr 72 of inhibitor 2, and sites 3b and 4 of glycogen synthase) contain a Ser/Thr flanked by a carboxyl-terminal proline. However, as MFPK did not phosphorylate a series of peptides containing the -X-Thr/Ser-Pro-X- sequence, this minimum consensus sequence is not sufficient for phosphorylation by MFPK.(ABSTRACT TRUNCATED AT 250 WORDS)
ATP Citrate (pro-S)-Lyase↗
An insulin-sensitive cytosolic protein kinase accounts for the regulation of ATP citrate-lyase phosphorylation.
Purified rat liver ATP citrate-lyase is phosphorylated on serine residues by an insulin-stimulated cytosolic kinase activity partially purified from rat adipocytes [Yu, Khalaf & Czech (1987) J. Biol. Chem. 262, 16677-16685]. The Km for lyase phosphorylation by this hormone-sensitive kinase activity is approx. 3 microM. Two-dimensional tryptic-peptide mapping of the 32P-labelled lyase reveals that the kinase-catalysed phosphorylation occurs primarily on a specific peptide. In intact 32P-labelled adipocytes, insulin enhances the serine phosphorylation of ATP citrate-lyase by 2-3-fold. Tryptic digestion of the 32P-labelled lyase immunopurified from insulin-treated adipocytes also yields one major phosphopeptide. 32P-labelled lyase tryptic peptides derived from labelling experiments in vitro and in vivo exhibit identical electrophoretic and chromatographic migration profiles. Furthermore, radio-sequencing of the phosphopeptide from lyase 32P-labelled in vitro indicates that serine-3 from the N-terminus is phosphorylated by the insulin-stimulated cytosolic kinase, in agreement with previous studies on the position of the phosphoserine residue in ATP citrate-lyase isolated from insulin-treated cells. Taken together, the similarity in site-specific phosphorylation of ATP citrate-lyase from insulin-treated adipocytes to that catalysed by the hormone-activated cytosolic kinase in vitro strongly suggests that this kinase mediates insulin action on lyase phosphorylation in intact cells.
ATP Citrate (pro-S)-Lyase↗
Effect of insulin on ATP-citrate lyase phosphorylation: regulation of peptide A and peptide B phosphorylations.
Insulin decreases multifunctional protein kinase (MFPK) activity in rat adipose tissue [Ramakrishna, S., & Benjamin, W. B. (1988) J. Biol. Chem. 263, 12677-12681]. Insulin also decreases the phosphorylation of peptide B but increases the phosphorylation of peptide A of ATP-citrate lyase (ATP-CL). The mechanism for this increase in peptide A phosphorylation was studied with purified ATP-CL from control and insulin- and isoproterenol-treated fat pads by using MFPK and the catalytic subunit of cAMP-dependent protein kinase (A-kinase). ATP-CL purified from insulin-treated fat pads is a better substrate for phosphorylation by MFPK compared to controls. This result is consistent with the hypothesis that insulin action decreases peptide B phosphorylation. To determine if the degree of phosphorylation at peptide B affects the phosphorylation rate of peptide A by A-kinase, ATP-CL was prepared with determined phosphate contents of peptides A and B. ATP-CL with a low phosphate content at peptide B is a better substrate for phosphorylation at peptide A by A-kinase than is ATP-CL with a high phosphate content at peptide B. These results suggest that the insulin-induced increase in ATP-CL phosphorylation at peptide A is due to a decrease in peptide B phosphorylation. ATP-CL prepared from isoproterenol-treated fat pads is also a better substrate for phosphorylation at peptide B by MFPK than controls. This increase in phosphorylation at peptide B by MFPK is due to positive second-site regulation by the isoproterenol-induced increase in peptide A phosphorylation.
ATP Citrate (pro-S)-Lyase↗
Insulin action rapidly decreases multifunctional protein kinase activity in rat adipose tissue.
ATP-citrate lyase in vivo contains three phosphorylation sites on two tryptic peptides (peptides A and B). These phosphorylation sites are under hormonal control. Multifunctional protein kinase (MFPK) from rat liver phosphorylates peptide B on serine and threonine residues whereas cAMP-dependent protein kinase phosphorylates peptide A on a serine residue (Ramakrishna, S., and Benjamin, W. B. (1985) J. Biol. Chem. 260, 12280-12286). We now report that rat adipose tissue MFPK also phosphorylates serine and threonine residues of peptide B of ATP-citrate lyase. When the activity of MFPK was assayed using partially purified (by chromatography on phosphocellulose) cytosol fractions from insulin-treated adipose tissue, it was found that MFPK activity was decreased by over 55%. This decrease in MFPK activity occurs at physiological concentrations of insulin (EC50 = 1 x 10(-10) M). Its onset is rapid and almost maximal at 5 min after the addition of insulin. Even when new protein synthesis is inhibited by cycloheximide, extracts from insulin-treated fat pads have less MFPK activity compared to the control. The insulin effect is maintained after further chromatography on a gel filtration column suggesting that the decrease in MFPK activity is not due to a low molecular weight inhibitor. The insulin-induced decrease in MFPK activity is due to a decrease in Vmax whereas the affinity of this enzyme toward ATP-citrate lyase or ATP is unchanged.
ATP Citrate (pro-S)-Lyase↗
Phosphorylation of sites 3 and 2 in rabbit skeletal muscle glycogen synthase by a multifunctional protein kinase (ATP-citrate lyase kinase).
A multifunctional protein kinase, purified from rat liver as ATP-citrate lyase kinase, has been identified as a glycogen synthase kinase. This kinase catalyzed incorporation of up to 1.5 mol of 32PO4/mol of synthase subunit associated with a decrease in the glycogen synthase activity ratio from 0.85 to a value of 0.15. Approximately 65-70% of the 32PO4 was incorporated into site 3 and 30-35% into site 2 as determined by reverse phase high performance liquid chromatography. Release of 32PO4 from the phosphopeptides during automated Edman degradation confirmed the site 3 and 2 assignment. Thermal stability studies established that the phosphorylations of sites 3 and 2 were catalyzed by the same kinase. This multifunctional kinase was distinguished from glycogen synthase kinase-3 on the basis of nucleotide (ATP versus GTP) and protein substrate (glycogen synthase, ATP-citrate lyase, and acetyl-CoA carboxylase) specificities. Since the phosphate contents in glycogen synthase of sites 3 and 2 are altered in diabetes and by insulin administration, the possible involvement of the multifunctional kinase was explored. Glycogen synthase purified from diabetic rabbits was phosphorylated in vitro by this multifunctional kinase at only 10% of the rate compared to synthase purified from control rabbits. Treatment of the diabetics with insulin restored the synthase to a form that was readily phosphorylated in vitro.
Animals↗
Cyclic nucleotide-independent protein kinase from rat liver. Purification and characterization of a multifunctional protein kinase.
A rat liver cAMP-independent protein kinase that phosphorylates peptide b of ATP-citrate lyase (Ramakrishna, S., Pucci, D. L., and Benjamin, W. B. (1983) J. Biol. Chem. 258, 4950-4956) has been purified to apparent homogeneity. The molecular weight, determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, sucrose density gradient, and by gel filtration, was found to be 36,000. This protein kinase phosphorylates in vitro ATP-citrate lyase, acetyl-CoA carboxylase, and glycogen synthase and does not phosphorylate phosphorylase, phosphorylase kinase, histone, phosvitin, and casein. It has Fa (activity factor) activity stimulating the ATP X Mg-dependent phosphatase and is therefore named a multifunctional protein kinase. This kinase differs from glycogen synthase kinase-3 with regard to substrate specificity, kinetic parameters, and physicochemical properties.
Animals↗
Insulin stimulates the dephosphorylation of phosphothreonine from fat-pad ATP-citrate lyase.
ATP-citrate lyase is phosphorylated in vivo at three amino acid residues on two peptide sequences (peptides a and b). Insulin action is known to increase the phosphorylation of peptide a. To study the effect of insulin on peptide b phosphorylation ATP-citrate lyase was radiolabeled in vivo by incubating fat pads with 32Pi. Following "cold chase", insulin action decreased the calculated specific radioactivity of peptide b to less than 30% of control whereas the specific radioactivity of peptide a increased 5-6 fold. The insulin induced decrease in peptide b phosphorylation was mainly due to a decrease in phosphothreonine phosphorylation. Isoproterenol treatment increased peptide a phosphorylation 4-6 fold but did not decrease peptide b phosphorylation. Specific radioactivity of ATP did not change significantly with hormone treatment. These results suggest that insulin action increases the dephosphorylation of peptide b by increasing the activity of a putative phosphothreonine phosphatase.
ATP Citrate (pro-S)-Lyase↗
Insulin stimulates phosphorylation of a heat-stable protein in rat adipose tissue.
Insulin in rat adipose tissue acts to increase the phosphorylation about 2.5-fold of a low molecular weight protein in the cytosol designated phosphoprotein m. Isoproterenol had no effect on the phosphorylation of phosphoprotein m. Some of the properties of phosphoprotein m are: soluble in 1% trichloro acetic acid, heat-stable and has a molecular weight of 23,000 on polyacrylamide gels in the presence of sodium dodecyl sulfate. Phosphoserine and phosphothreonine are the phosphorylated amino acid residues of phosphoprotein m. The physical and chemical properties of phosphoprotein m are similar to those of previously described inhibitor and modulator proteins.
Adipose Tissue↗
Phosphorylation of different sites of acetyl CoA carboxylase by ATP-citrate lyase kinase and cyclic AMP-dependent protein kinase.
Native acetyl CoA carboxylase was phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase and ATP-citrate lyase kinase to 1 and 0.5 mol/subunit respectively. Both protein kinases added together increased acetyl CoA carboxylase phosphorylation additively. Partial proteolysis of 32P-acetyl CoA carboxylase followed by electrophoretic analysis showed that the 32P-phosphopeptides generated from acetyl CoA carboxylase phosphorylated with lyase kinase were different from the peptides obtained from the enzyme phosphorylated by cyclic AMP-dependent protein kinase. Mapping of tryptic 32P-phosphopeptides by high performance liquid chromatography showed that the major phosphopeptides phosphorylated by ATP-citrate lyase kinase were different from the major phosphopeptides phosphorylated by cyclic AMP-dependent protein kinase. The results suggest that at least one different site on acetyl CoA carboxylase is preferentially phosphorylated by each protein kinase.
Acetyl-CoA Carboxylase↗
ATP-citrate lyase phosphorylation in rat adipose tissue.
Previous in vitro studies demonstrated that ATP-citrate lyase is phosphorylated by cyclic AMP-dependent protein kinase at peptide A, containing a phosphoserine residue, and by ATP-citrate lyase kinase at peptide B, containing both phosphoserine and phosphothreonine residues (Ramakrishna, S., Pucci, D. L., and Benjamin, W. B. (1983) J. Biol. Chem. 258, 4950-4956). In the present study, trypsin-digested, radiolabeled ATP-citrate lyase from rat epididymal fat pads was analyzed by high performance liquid chromatography. Phosphorylation occurred at three amino acid residues within two different peptide sequences; one (peptide a) contained phosphoserine and the other (peptide b) contained phosphoserine and phosphothreonine. The retention times and molecular weights were the same for peptides a and A and peptides b and B. Isoproterenol action increased peptide a phosphorylation and, to a lesser extent, peptide b phosphorylation. Insulin action also increased peptide a phosphorylation, but did not increase peptide b phosphorylation.
ATP Citrate (pro-S)-Lyase↗
Dependence of ATP-citrate lyase kinase activity on the phosphorylation of ATP-citrate lyase by cyclic AMP-dependent protein kinase.
ATP-citrate lyase from rat liver and adipose tissue is phosphorylated by either ATP-citrate lyase kinase or catalytic subunit of cyclic AMP-dependent protein kinase to 0.5-0.6 mol/subunit. We previously demonstrated that the site phosphorylated by ATP-citrate lyase kinase (peptide B) is different from that phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase (peptide A) (Ramakrishna, S., Pucci, D. L., and Benjamin, W.B. (1981) J. Biol. Chem. 256, 10213-10216). ATP-citrate lyase phosphorylation by both protein kinases added simultaneously was increased synergistically. When ATP-citrate lyase was first phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase, the net phosphorylation of the fragments subsequently phosphorylated by lyase kinase increased about 6-fold. However, when ATP-citrate lyase was first phosphorylated by lyase kinase, there was no effect on the subsequent phosphorylation of the enzyme by cyclic AMP-dependent protein kinase. Alkaline phosphatase-dephosphorylated ATP-citrate lyase was phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase to 0.9-1.0 mol/subunit. However, dephospho-ATP-citrate lyase was not phosphorylated by lyase kinase. The addition of both protein kinases simultaneously phosphorylated ATP-citrate lyase up to 2 mol/subunit. Phosphorylation of dephospho-ATP-citrate lyase first by catalytic subunit of cyclic AMP-dependent protein kinase and ATP enabled the lyase to be phosphorylated by lyase kinase. Peptide mapping and phosphoamino acid analysis of dephospho-ATP-citrate lyase phosphorylated by catalytic subunit of cyclic AMP-dependent protein kinase and/or lyase kinase conclusively showed that phosphorylation of ATP-citrate lyase by ATP-citrate lyase kinase was completely dependent on peptide A phosphorylation by cyclic AMP-dependent protein kinase. Furthermore, increased phosphorylation when both protein kinases were added simultaneously was due to increased phosphorylation at peptide B.
ATP Citrate (pro-S)-Lyase↗
Rapid purification of enzymes of fatty acid biosynthesis from rat adipose tissue.
Acetyl CoA carboxylase, ATP-citrate lyase and fatty acid synthetase were purified to homogeneity by a simple procedure. The purification method consists of polymerization of acetyl CoA carboxylase with citrate followed by avidin-Sepharose affinity chromatography. ATP-citrate lyase and fatty acid synthetase were isolated as by-products of acetyl CoA carboxylase purification and are separated from each other by chromatography on DE-52. ATP-citrate lyase was further purified by CoA-agarose affinity chromatography and fatty acid synthetase was purified on Bio-Gel A-1.5m. Purified ATP-citrate lyase, acetyl CoA carboxylase and fatty acid synthetase had specific activities of 9.9, 2.8 and 1.8 U/mg respectively with an over all recovery of 30, 25 and 50% respectively. Using these purified enzymes, we found that ATP-citrate lyase and acetyl CoA carboxylase were phosphorylated in vitro by both cAMP-dependent protein kinase and ATP-citrate lyase kinase whereas fatty acid synthetase was not phosphorylated by these protein kinases.
ATP Citrate (pro-S)-Lyase↗