Sequencing of phosphoserine‐containing peptides yields normally no identifiable PTH‐derivatives at those positions where phosphoserine is located. Here a new method is described which allows identification of the position of phosphoserine by chemical modification just before sequence analysis. In a one‐step microbatch reaction, phosphoserine present in the intact peptide can be transformed quantitatively into stable derivatives such as β‐methylaminoalanine (MAA), S‐ethanolcysteine or S‐ethylcysteine. These derivatives are detectable during microsequencing with less than 100 pmol peptide using an Applied Biosystems gas‐phase sequencer equipped with an on‐line PTH amino acid analyzer.

Polyphosphoinositides are involved in many signal transduction pathways in eukaryotic cells. The first committed step is catalysed by phosphatidylinositol 4-kinase leading to the formation of phosphatidylinositol 4-phosphate. In the last four years, ten cDNA molecules have been cloned which code isoforms of phosphatidylinositol 4-kinase; some of which are highly related. Characteristically, they contain a C-terminal catalytic domain which is similar to that of (poly)phosphoinositide 3-kinases and to that of more distantly related lipid/protein kinases. Alignment has characterised cDNAs from Chaenorabditis, Dictyostelium and Schizostaphyloccus pombe as those of phosphatidylinositol 4-kinases also. All these lipid kinases are related to the superfamily of protein kinases. Several amino acids are highly conserved in catalytic domains of lipid and protein kinases. Employing the catalytic subunit of the cAMPdependent protein kinase as template, these residues can be assigned functionally. On the basis of the alignment, a phylogenetic tree of the superfamily of phosphatidylinositol kinases has been constructed. Three families, the phosphatidylinositol 4-kinases, phosphoinositide 3-kinases, and the phosphatidylinositol related lipid/protein kinases, can be recognised. Each family comprises two subfamilies. The involvement of the phosphatidylinositol 4-kinases in signal transduction processes is summarised and a new hypothesis for the function of their isoforms in polyphosphoinositide signalling is presented. The involvement of phosphatidylinositol 4-kinases in formation of lipidϪprotein interactions with cytoskeleton proteins and the metabolism of polyphosphoinositide in the nucleus is discussed.Keywords : phosphatidylinositol 4-kinase; types and genes of phosphatidylinositol 4-kinases; domain structure ; phylogeny; inositide phospholipid signaling; phosphatidylinositol 4,5-bisphosphate; phosphatidylinositol 4-phosphate ; vesicular traffic; phosphatidylinositol transfer protein.The phosphatidylinositol cycle (Hokin and Hokin, 1953), an the hydrophobic backbone, diacylglycerol, activates protein kinase C (Mitchell et al., 1991; Clapham, 1995). In eukaryotes increase in receptor-stimulated polyphosphoinositide turnover, has been in the focus of attention for more than four decades. A this is one of the most commonly used signalling pathways in a wide range of cells and may be surpassed only by cAMP which highlight was the discovery of two second messengers, inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3] and diacylglycerol, which are is used also in prokaryotes (de Gunzburg, 1985).In the last decade, it has become increasingly clear that polyproduced from phosphatidylinositol 4,5-bisphosphate (PtdInsP 2 ) by phospholipase C (PLC). The hydrophilic headgroup, phosphoinositides cover a wider variety of functions other than just being second-messenger precursors. In addition to being Ins(1,4,5)P 3, mobilises Ca 2ϩ from intracellular stores whereas phosphorylated at the D4 and D5 positions of the inositol ring, arrangement (Whit...

Isolated skeletal muscle triads contain a compartmentalized glycolytic reaction sequence catalyzed by aldolase, triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate kinase. These enzymes express activity in the structure-associated state leading to synthesis of ATP in the triadic junction upon supply of glyceraldehyde 3-phosphate or fructose 1,6-bisphosphate. ATP formation occurs transiently and appears to be kinetically compartmentalized, i.e., the synthesized ATP is not in equilibrium with the bulk ATP. The apparent rate constants of the aldolase and the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase reaction are significantly increased when fructose 1,6-bisphosphate instead of glyceraldehyde 3-phosphate is employed as substrate. The observations suggest that fructose 1,6-bisphosphate is especially effectively channelled into the junctional gap. The amplitude of the ATP transient is decreasing with increasing free [Ca2+] in the range of 1 nM to 30 microM. In the presence of fluoride, the ATP transient is significantly enhanced and its declining phase is substantially retarded. This observation suggests utilization of endogenously synthesized ATP in part by structure associated protein kinases and phosphatases which is confirmed by the detection of phosphorylated triadic proteins after gel electrophoresis and autoradiography. Endogenous protein kinases phosphorylate proteins of apparent Mr 450,000, 180,000, 160,000, 145,000, 135,000, 90,000, 54,000, 51,000, and 20,000, respectively. Some of these phosphorylated polypeptides are in the Mr range of known phosphoproteins involved in excitation-contraction coupling of skeletal muscle, which might give a first hint at the functional importance of the sequential glycolytic reactions compartmentalized in triads.

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We have cloned cDNA molecules encoding the P subunit of phosphorylase kinase (ATP:phosphorylase-b phosphotransferase; EC 2.7.1.38) from rabbit fast-twitch skeletal muscle and have determined the complete primary structure of the polypeptide by a combination of peptide and DNA sequencing. In the mature 13 subunit, the initial methionine is replaced by an acetyl group. The subunit is composed of 1092 amino acids and has a calculated molecular mass of 125,205 Da. Alignment of its sequence with the a subunit of phosphorylase kinase reveals extensive regions of homology, but each molecule also possesses unique sequences. Two of the three phosphorylation sites known for the P subunit and all seven phosphorylation sites known for the a subunit are located in these unique domains.

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From rabbit and human cardiac troponin I N‐terminal mono and bisphosphorylated peptides were isolated which were obtained from Lys‐C proteinase digests. Two adjacent phosphoserine residues could be localized in each phosphopeptide following further tryptic digestion. The previously published sequence of rabbit cardiac troponin I had to be corrected. Two adjacent phosphoserine residues are a common motif in the very similar sequences of bovine, rabbit and human cardiac troponin I. The N‐terminal sequences are: AcADRSGGSTAG DTVPAPPPVR RR ANYRAY ATEPHAK (bovine), AcADESTDA‐AG EARPAPAPVR RRANYRAY ATEPHAK (rabbit), (Ac,A,D/N,G,S,S,D/N,A,A,R) EPRPAPAPIR RR‐NYRAY ATEPHAK (human).

If the degree of substitution of Sepharose 4 B with alpha-alkylamines is varied gels of different hydrophobicity are produced. Proteins can be adsorbed when a critical hydrophobicity (ca. 10-12 alkyl residues/Sepharose sphere) is reached. The enzymes phosphorylase kinase, phosphorylase phosphatase, 3',5'-cAMP dependent protein kinase, glycogen synthetase, and phosphorylase b are successively adsorbed as the hydrophobicity of the Sepharose is increased. The capacity of the gels for these enzymes and protein in general increases exponentially reaches plateau values as a function of the degree of substitution. There is no indication of a restriction of the hydrophobic centers for a given protein. The critical hydrophobicity needed to adsorb proteins can either be otained in the above manner or by elongation of the employed alkylamine at a constant degree of substitution. Additonally, as the hydrophobicity of a gel is increased higher binding forces result and desorption of proteins requires an augmentation of the salt concentration in the elution buffer. Elution of proteins from a hydrophobic matrix can be described in terms of salting-in phenomena since desorption is dependent on the type of salt employed and not on the ionic strength alone. This also rules out ionic interactions as a major factor in adsorption per se. By rationally controlling the hydrophobicity of a Sepharose gel the adsorption and elution of a protein may be thus establised that its purification or elimination can be optimally performed.