Light modulation of chloroplast membrane-bound ferredoxin-NADP+ oxidoreductase.

Publisher Summary Protein phosphorylation and dephosphorylation are well recognized as major metabolic control mechanisms in eukaryotic cells. By the 1940s, through work in the laboratories of Con and others, the basic biochemistry of glycogen breakdown had been established with the characterization of the phosphorylase-catalyzed conversion of glycogen to glucose 1-phosphate. This chapter discusses the extensive network of regulatory phenomena that impinge upon the control of phosphorylase kinase activity. Phosphorylase kinase activity can be modulated by a number of effectors that interact in a noncovalent and specific manner and presumably modulate activity by affecting the enzyme's conformation. Included in this group are Ca 2+ , Mg 2+ , calmodulin, and glycogen; each is discussed in the chapter. It is suggested that the understanding of the control of glycogenolysis has served well for many years as a guideline for how other metabolic control systems may function. Similarly, phosphorylase kinase can serve as a model to understand the properties of other regulatory enzymes. An attempt is made in this chapter to provide this understanding.

10 Phosphorylase Kinase

Bovine cardiac troponin isolated in a highly phosphorylated form shows four 31P-NMR signals [Beier, N., Jaquet, K., Schnackerz, K. & Heilmeyer, L. M. G. Jr (1988) Eur. J. Biochem. 176, 327–334]. Troponin I, which contains phosphate covalently linked to serine-23 and/or-24 [Swiderek, K., Jaquet, K., Meyer, H. E. & Heilmeyer, L. M. G. Jr (1988) Eur. J. Biochem. 176, 335–342], shows three resonances. Mg2+-saturation of holotroponin shifts these troponin I resonances to higher fields. Direct binding of Mg2+ to the phosphate groups can be excluded. Both these serine residues of troponin I, 23 and 24, are substrates for cAMP- and cGMP-dependent protein kinases as well as for protein kinase C.



Isolated bovine cardiac troponin T contains 1.5 mol phosphoserine/mol protein, indicating that minimally two serine residues are phosphorylated. One phosphoserine residue is located at the N-terminus. An additional phosphoserine is located in the C-terminal cyanogen bromide fragment, CN4, which contains covalently bound phosphate. Protein kinase C phosphorylates serine-194, thus demonstrating exposure of this residue on the surface of holotroponin.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1990.tb15612.x

Sites phosphorylated in bovine cardiac troponin T and I. Characterization by 31P-NMR spectroscopy and phosphorylation by protein kinases.

Synergistic activation by Ca2+ and Mg2+ as the primary cause for hysteresis in the phosphorylase kinase reactions.

Rabbit skeletal muscle phosphorylase kinase. Catalytic and regulatory properties of the active alpha gamma delta and gamma delta complexes.

Novel aspects of skeletal muscle protein kinase and protein phosphatase regulation by Ca2

Phosphorylase kinase, (αβγδ)4, binds in two subsequent steps 2 mol Ca2+/monomer (αβγδ) to high affinity sites, N1a, and 1–2 mol to low affinity sites, N2. Analogously, the holotroponin TI2C binds 2 mol Ca2+ to high affinity and further 2 mol to low affinity sites. In both protein complexes Ca2+ binds to one specific subunit: in phosphorylase kinase to the δ- and in troponin TI2C to the C-subunit. In both proteins the high affinity sites show Ca2+-Mg2+ competition. Cooperative interactions are observable at the low affinity Mg2+ inducible sites in phosphorylase kinase and at the high affinity sites in troponin. The isolated δ subunit binds 2 mol Ca2+ with low affinity in a positive cooperative manner. Ca2+ binding to the high affinity sites inhibits the phosphorylation of the I subunits of troponin but stimulates that of the α and β subunits of phosphorylase kinase. Phosphorylase kinase exhibits three partial activities: A0, A1 and A2. A0 is Ca2+ independent whereas activation of A1 can be correlated to Ca2+ binding to the sites, N1a, and activation of A2 with Ca2+ binding to the sites, N2. Both Ca2+ binding proteins, δ and troponin C, can activate the kinase activity of calsequestrin which is a membrane component of the sarcoplasmic reticulum.

Troponin C and calcium dependent regulator protein, two ancestral skeletal muscle calcium binding proteins.

The degree of phosphorylation of a protein should correlate with a meaningful change of a functional property if this process is of physiological importance (Krebs and Beavo 1979). Thus, it would require that the introduced phosphate group perturbs interaction of peptide domaines within a polypeptide or between subunits. The phosphate group itself may be used as a reporter group to monitor such perturbations since it yields a [31P] NMR signal which is sensitive to its environment. Therefore the [31P] NMR spectra of phosphorylated skeletal muscle troponin and myosin will be compared with that of phosphorylase a (see also Sperling et al. 1979; Koppitz et al. 1980). It will be shown that these phosphoproteins can be classified into two types according to the appearance of their [31P] NMR signals.

K.P. Kohse

Papers

Novel aspects of skeletal muscle protein kinase and protein phosphatase regulation by Ca2

Troponin C and calcium dependent regulator protein, two ancestral skeletal muscle calcium binding proteins.

Control of Mg2+ and Ca2+ Binding to Troponin C and Calmodulin by Phosphorylation of the Respective Holocomplexes Troponin and Phosphorylase Kinase