Multiple forms of phosphofructokinase in developing rabbit and guinea pig tissues.

Multiple forms of phosphofructokinase in striated muscle and cardiac muscle of developing rabbit (Oryctolagus cuniculus) undergo changes with development, but not in brain and liver. The cardiac muscle of the 1-day-old rabbit contains phosphofructokinase A₄ together with the four hybrid forms which were tentatively called A₃C, A₂C₂, AC₃, and C₄. In older animals, phosphofructokinase C₄ disappears first, followed by the hybrid forms, and only phosphofructokinase A₄ persists in the adult animal. Both phosphofructokinase A₄ and phosphofructokinase C₄, as well as their hybrid forms, are present in developing embryonic brain and also in the brains of adult animals. Developing rabbit liver contains a single form of phosphofructokinase, but two isoenzymes are consistently seen in guinea pig liver. In striated muscle from fetal and 1-day-old rabbit, two isoenzymes are found, tentatively identified as A₄ and the A₃C hybrid. The results suggest that fetal phosphofructokinase A₄ and phosphofructokinase C₄, and their hybrids, might be present in striated muscle. Guinea pig tissues show a pattern of phosphofructokinase isoenzymes different from that in rabbit tissues.     

Multiple forms of rat dentin phosphoproteins

Previous studies have shown that the phosphoprotein from rat dentin is heterogenous and can be partially separated into two fractions by ion-exchange chromatography. These proteins were further characterized by polyacrylamide gel electrophoresis, gel chromatography, and amino acid and phosphate analysis, after chromatographic separations on ion-exchange columns. On 5-15% gradient gels, the phosphoproteins extracted from rat dentin and precipitated by CaCl2 gave three Alcian blue-staining bands with apparent molecular weights in the 90-95,000 range. The two slower-moving bands corresponded to highly phosphorylated proteins (HP) that had phosphoserine contents of greater than 400 residues per thousand and contained little or no valine, leucine, phenylalanine, or arginine. The faster-moving band corresponded to a moderately phosphorylated protein that contained about 250 residues per thousand of phosphoserine and greater quantities of glutamic acid, proline, and several other amino acids than HP. The nature of the phosphoproteins in HP was further studied after total removal of the phosphate with an insoluble form of bovine intestinal alkaline phosphatase. The dephosphorylated product (dP-HP) gave a single major band on gel electrophoresis but showed evidence for two closely related NH2-terminal sequences, Asp-Asp-Asp-Asn and Asp-Asp-Pro-Asn. The dephosphorylated material was separated into two components (dP-HP1 and dP-HP2) by chromatography on QAE-Sephadex A-25. The amino acid compositions of the two components showed that they differed in their primary structures. This conclusion was verified by the finding of the proline-containing sequence in dP-HP2. In addition to these two groups of phosphoproteins, a third class, LP, contains low levels of phosphoserine and high amounts of glutamic acid (W.T. Butler, M. Bhown, M.T. DiMuzio, and A. Linde, (1981) Coll. Res. 1, 187-199).     

The effect of cyclic GMP on phosphofructokinase from rat tissues.

In view of the recently proposed hypothesis of biologic regulation through opposing influences of cyclic AMP and cyclic GMP, and since cyclic AMP is a well-known allosteric activator of phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11), the effect of cyclic GMP on the activity of this enzyme from several rat tissues was investigated. It was found that cyclic GMP exerted an inhibitory effect on the activity of rat heart and skeletal muscle phosphofructokinase. This effect was most pronounced under conditions in which the enzyme was partially inhibited by ATP or by citrate. Cyclic GMP also antagonized the deinhibitory action of cyclic AMP and other allosteric activators, such as glucose 1,6-bisphosphate or AMP, on the ATP or citrate-inhibited heart or muscle phosphofructokinase. In contrast to the heart and skeletal muscle phosphofructokinase, the adipose-tissue enzyme was not affected by cyclic GMP to any significant degree. The antagonistic action of cyclic GMP to the activation of heart-phosphofructokinase, may suggest a mechanism by which the activity of phosphofructokinase is synchronized with the activity of glycogen phosphorylase, as a result of acetylcholine action in heart, to achieve a decrease in total glycogenolysis and glycolysis.     

Multiple forms of protein phosphatase inhibitors in mammalian tissues.

The heat-stable inhibitors of phosphorylase phosphatase from rat skeletal muscle, rat liver, beef heart, and beef adrenal cortex were studied. Two major types of inhibitors can be separated from all these tissues by chromatography on DEAE-cellulose. The two types of inhibitors from rat muscle are the same as those reported for rabbit muscle. The type-1 inhibitor, but not the type-2, is regulated by phosphorylation and dephosphorylation reactions. There is also a phosphorylatable inhibitor in beef heart and adrenal cortex, but such an inhibitor could not be demonstrated in liver.     

Multiple forms of rat liver cysteinesulfinate decarboxylase

Cysteinesulfinate decarboxylase, purified from male rat livers and homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is resolved into five distinct enzyme species (isoforms) by gel isoelectric focusing. Since the isoforms are present in fresh liver homogenates and do not arise by proteolysis, the enzyme is apparently heterogeneous in vivo. Although female rat livers contain only 5% of the cysteinesulfinate decarboxylase activity of male livers, immunological and enzymatic studies indicate that the distribution of isoforms is similar in both sexes. Rat brain and kidney also contain multiple isoforms which are cross-reactive with polyclonal antibodies prepared to the liver enzyme. The enzyme exhibits a protomer Mr of 53,000, and the native enzyme is shown by cross-linking studies to be dimeric. Purified enzyme contains no carbohydrate or phosphate and does not bind excess pyridoxal 5'-phosphate. Two pools of enzyme activity are resolved preparatively by chromatofocusing chromatography and have been examined with respect to substrate and inhibitor specificity. Both pools are most active toward L-cysteinesulfinate and L-cysteinesulfonate. Aspartate, homocysteinesulfinate, homocysteinesulfonate, 2-amino-3-phosphonopropionate, and glutamate are decarboxylated at rates less than 1% of that observed with L-cysteinesulfinate; D-cysteinesulfinate is not decarboxylated but is an effective inhibitor. The enzyme isoforms cannot be distinguished on the basis of substrate affinity or specificity. The enzyme is irreversibly inactivated by the mechanism-based inhibitors beta-methylene-DL-aspartate and beta-ethylidene-DL-aspartate. beta-Ethylideneaspartate, in contrast to the beta-methylene derivative, does not inhibit aspartate aminotransferase, an enzyme also important in cysteinesulfinate metabolism. beta-Ethylidene aspartate or related beta-ethylidene compounds may be useful in selectively altering cysteinesulfinate metabolism in vivo.     

Multiple molecular forms of rat brain enkephalinase

Rat brain enkephalinase has been partially purified by ion exchange chromatography, chromatofocusing, and affinity chromatography on immobilized lectins. Ion exchange chromatography resolved two principle forms of enkephalinase designated A1 and A2. Both enkephalinase A1 and A2 are bound to immobilized lentil lectin while chromatography on immobilized wheat germ lectin resolved each of the principle forms into two subforms, A1, 1, A1, 2, A2, 1, and A2, 2. All four enkephalinase forms have similar, if not identical kinetic properties. The possible implications of multiple molecular forms of enkephalinases are discussed.     

Multiple forms of immunoreactive dynorphin in rat pituitary and brain

Multiple forms of immunoreactive dynorphin (I-dynorphin) in rat anterior pituitary (AP), intermediate-posterior pituitary (IP) and medial basal hypothalamus (MBH) were examined. Three I-dynorphin peaks were observed on gel filtration. The first peak (big form) was eluted near the position of beta-LPH, and was predominant in AP. The second peak (middle form) was eluted near the position of ACTH. The third peak (small form) was eluted at the position of dynorphin (1-13), ane was predominant in IP and MBH. The heterogeneity of this small form was examined by ion exchange chromatography and reverse phase high performance liquified chromatography (HPLC). I-dynorphin peaks were observed at the positions of dynorphin(1-17), (1-13), (1-11), (1-10) and other peptides. These results strongly suggest (i) the presence of dynorphin(1-17), (1-13), (1-11) and (1-10) in rat IP, (ii) dynorphin(1-11) and (1-10) as the major components in this small form, (iii) the difference of I-dynorphin processing in AP, IP and MBH.     

Multiple forms of rat liver L-asparagine synthetase.

Addition of NaF or MFP to rat hepatocytes resulted in a decrease in lactate and in an increase in glucose, 3 and 2-phosphoglycerate production. When dihydroxyacetone was present in the incubation medium both NaF and MFP increased the production of glucose, fructose-1,6-diphosphate, 3 and 2 phosphoglycerate, with a decrease in pyruvate and lactate. In the presence of lactate, glucose production increased only in the presence of MFP, but there was a 8–10 fold increase in the level of phosphoenol pyruvate with both NaF and MFP. The crossover data indicated that the activity of some of the glycolytic enzymes may be inhibited in the presence of NaF and MFP.     

Differences in the allosteric properties of pure low and high phosphate forms of phosphofructokinase from rat liver

Low phosphate and high phosphate forms of phosphofructokinase (Furuya, E., and Uyeda, K. (1980) J. Biol. Chem. 255, 11656-11659) from rat liver were purified to homogeneity and various properties were compared. The specific activities of these enzymes and their electrophoretic mobilities on polyacrylamide in sodium dodecyl sulfate are the same. A limited tryptic digestion yields products with no change in the enzyme activity but with a reduction in the molecular weight of about 2000. Both low and high phosphate enzymes can be phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, and approximately twice as much [32P]phosphate is incorporated into the low phosphate than the high phosphate enzyme. A comparison of their allosteric kinetic properties reveal that the high phosphate enzyme is much more sensitive to inhibition by ATP and citrate and shows a higher K0.5 for fructose 6-phosphate than the low phosphate enzyme, and the difference in the K0.5 values becomes greater at lower pH values. Furthermore, the high phosphate phosphofructokinase is less sensitive to activation by AMP and fructose 2,6-bisphosphate. Moreover, when the low phosphate enzyme is phosphorylated by protein kinase, the resulting phosphorylated enzyme exhibits a higher K0.5 for fructose 2,6-bisphosphate than does the untreated enzyme. These results demonstrate that the phosphorylation affects the allosteric kinetic properties of the enzyme and results in a less active form of phosphofructokinase.     

Multiple forms of uridine kinase in normal and neoplastic rat liver

Two species of uridine kinase with molecular weights of approximately 120000 (I) and 30000 (II) have been identified in the rat liver system. Species I predominates in the 7-day postnatal and adult rat liver and increases in the regenerating remnant of the latter after partial hepatectomy; the concentration of species II is low in these tissues. Species I also predominates in the slow-growing hepatomas 5123D and 7800. In contrast, II is the predominant form in the foetal rat liver and accounts for 40% of the total activity in the rapidly growing Novikoff ascites hepatoma. In contrast to species II, which was stable, species I was inactivated by preincubation for 30min at 37 degrees C, before assay at 23 degrees C.