Ngk1 kinase-mediated N-acetylglucosamine metabolism promotes UDP-GlcNAc biosynthesis in Saccharomyces cerevisiae

N-acetylglucosamine (GlcNAc) is an important structural component of the cell wall chitin, N-glycans, glycolipids, and GPI-anchors in eukaryotes. GlcNAc kinase phosphorylates GlcNAc into GlcNAc-6-phosphate, a precursor of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) that serves as a substrate for glycan synthesis. Although GlcNAc kinase is found widely in organisms ranging from microorganisms to mammals, it has never been found in the model yeast Saccharomyces cerevisiae. Here, we demonstrate the presence of GlcNAc metabolism for UDP-GlcNAc biosynthesis in S. cerevisiae through Ngk1, a GlcNAc kinase we discovered previously. The overexpression or deletion of Ngk1 in the presence of GlcNAc affected the amount of both UDP-GlcNAc and chitin, suggesting that GlcNAc metabolism via Ngk1 promotes UDP-GlcNAc synthesis. Our data suggest that the Ngk1-mediated GlcNAc metabolism compensates for the hexosamine pathway, a known pathway for UDP-GlcNAc synthesis.

Profiles of central nervous system surgical site infections in endoscopic transnasal surgery exposing the intradural space

OBJECTIVE

Despite its efficacy and minimal invasiveness, the clean-contaminated nature of endoscopic transnasal surgery (ETS) may be susceptible to central nervous system surgical site infections (CNS-SSIs), especially when involving intradural exposure. However, the profiles of ETS-associated CNS-SSIs are not fully elucidated.

METHODS

The institutional ETS cases performed between May 2017 and March 2023 were retrospectively analysed. The incidences of CNS-SSIs were calculated, and their risk factors examined.

RESULTS

The incidence of CNS-SSIs was 2.3% (7/305) in the entire cohort and 5.0% (7/140) in ETSs with intradural exposure. All the CNS-SSIs were meningitis and developed following ETS with intradural exposure. The incidences were 0%, 5.6% and 5.8% in ETSs with Esposito grade 1, 2 and 3 intraoperative cerebrospinal fluid leakage, respectively. Among the pre- and intra-operative factors, body mass index (unit odds ratio (OR), 0.62; 95% confidence interval (CI), 0.44-0.89; P<0.01), serum albumin (unit OR, 0.03; 95% CI, 0.0007-0.92; P=0.02), and American Society of Anesthesiologists physical status score (unit OR, 20.7; 95% CI, 1.65-259; P<0.01) were significantly associated with CNS-SSIs. Moreover, postoperative cerebrospinal fluid leakage was also significantly associated with CNS-SSIs (OR, 18.4; 95% CI, 3.55-95.0; P<0.01).

CONCLUSIONS

The incidence of ETS-associated CNS-SSIs is acceptably low. Intradural exposure was a prerequisite for CNS-SSIs. Malnutrition and poor comorbidity status should be recognized as important risks for CNS-SSIs in ETS.

A C1/C4-oxidizing AA10 Lytic Polysaccharide Monooxygenase from <i>Paenibacillus xylaniclasticus</i> strain TW1

Lytic polysaccharide monooxygenases (LPMO) are key enzymes for the efficient degradation of lignocellulose biomass with cellulases. A lignocellulose-degradative strain, Paenibacillus xylaniclasticus TW1, has LPMO-encoding PxAA10A gene. Neither the C1/C4-oxidizing selectivity nor the enzyme activity of PxAA10A has ever been characterized. In this study, the C1/C4-oxidizing selectivity of PxAA10A and the boosting effect for cellulose degradation with a cellulase cocktail were investigated. The full-length PxAA10A (rPxAA10A) and the catalytic domain (rPxAA10A-CD) were heterologously expressed in Escherichia coli and purified. To identify the C1/C4-oxidizing selectivity of PxAA10A, cellohexaose was used as a substrate with the use of rPxAA10A-CD, and the products were analyzed by MALDI-TOF/MS. As a result, aldonic acid cellotetraose and cellotetraose, the products from C1-oxidization and C4-oxidization, respectively, were detected. These results indicate that PxAA10A is a C1/C4-oxidizing LPMO. It was also found that the addition of rPxAA10A into a cellulase cocktail enhanced the cellulose-degradation efficiency.

Characterization of a GH family 43 β-xylosidase having a novel carbohydrate-binding module from <i>Paenibacillus xylaniclasticus</i> strain TW1

Paenibacillus xylaniclasticus strain TW1, a gram-positive facultative anaerobic bacterium, was isolated as a xylanolytic microorganism from the wastes of a pineapple processing factory. A gene encoding one of its xylanolytic enzymes, a β-xylosidase, was cloned and sequenced. Sequence analysis revealed that this β-xylosidase, named PxXyl43A, was composed of a glycoside hydrolase (GH) family 43 subfamily 12 catalytic module and an unknown function module (UM). The full-length PxXyl43A (PxXyl43A) was heterologously expressed in Escherichia coli and purified. Recombinant PxXyl43A exhibited hydrolysis activity against both p-nitrophenyl-β-D-xylopyranoside (pNPX) and p-nitrophenyl-α-L-arabinofuranoside at specific activities of 250 and 310 mU/mg, respectively. The optimal reaction pH and temperature for pNPX hydrolysis were 7.1 and 54 ˚C, respectively. At pH 7.0 and 54 ˚C, the K_m and k_cat for pNPX were 1.2 mM and 2.8 ± 0.15 s^-1, respectively. It was also discovered that the recombinant unknown function module of PxXyl43A (PxXyl43A-UM) could bind to insoluble xylans like birchwood xylan and oat spelt xylan, whereas it did not bind to cellulosic substrates such as ball-milled cellulose, carboxymethyl cellulose or lichenan. The PxXyl43A-UM's binding constant value K_a for oat spelt xylan was 2.0 × 10^-5 M^-1. These results suggest that PxXyl43A possesses a novel carbohydrate-binding module, named as CBM91, specific for xylan-containing polysaccharides.

The Emi2 Protein of Saccharomyces cerevisiae is a Hexokinase Expressed under Glucose Limitation

Hexokinases catalyze glucose phosphorylation at the first step in glycolysis in eukaryotes. In the budding yeast Saccharomyces cerevisiae , three enzymes for glucose phosphorylation have long been known: Hxk1, Hxk2, and Glk1. In this study, we focus on Emi2, a previously uncharacterized hexokinase-like protein of S. cerevisiae . Our data show that the recombinant Emi2 protein (rEmi2), expressed in Escherichia coli , possesses glucose-phosphorylating activity in the presence of ATP and Mg ²⁺ . It was also found that rEmi2 phosphorylates not only glucose but also fructose, mannose and glucosamine in vitro . In addition, we examined changes in the level of endogenous Emi2 protein in S. cerevisiae in the presence or absence of glucose and a non-fermentable carbon source. We found that the expression of Emi2 protein is tightly suppressed during proliferation in high glucose, while it is strongly upregulated in response to glucose limitation and the presence of a non-fermentable carbon source. Our data suggest that the expression of the endogenous Emi2 protein in S. cerevisiae is regulated under the control of Hxk2 in response to glucose availability in the environment.

Chemo-enzymatic synthesis of the glucagon containing N-linked oligosaccharide and its characterization

The chemo-enzymatic synthesis of an artificially N-glycosylated derivative of glucagon, a peptide hormone that regulates the blood sugar level, is described. We synthesized the glycosylated glucagon by chemical synthesis of an N-acetylglucosaminyl peptide and enzymatic transfer of an oligosaccharide using the transglycosylation activity of the glycosynthase-like mutant of Mucor hiemalis endo-β-N-acetylglucosaminidase (Endo-M) and sialo-oligosaccharide oxazoline as a donor substrate. The sialo-oligosaccharide-attached glucagon synthesized showed high resistance against protease degradation and stimulated the release of glucose from mouse hepatocytes when added to cells. The synthetic glucagon showed slightly higher activity than native glucagon and has potential as a therapeutic agent for treating diabetic patients.

Ecm33 is a novel factor involved in efficient glucose uptake for nutrition-responsive TORC1 signaling in yeast

Glucose uptake is crucial for providing both an energy source and a signal that regulates cell proliferation. Therefore, it is important to clarify the mechanisms underlying glucose uptake and its transmission to intracellular signaling pathways. In this study, we searched for a novel regulatory factor involved in glucose-induced signaling by using Saccharomyces cerevisiae as a eukaryotic model. Requirement of the extracellular protein Ecm33 in efficient glucose uptake and full activation of the nutrient-responsive TOR kinase complex 1 (TORC1) signaling pathway is shown. Cells lacking Ecm33 elicit a series of starvation-induced pathways even in the presence of extracellular high glucose concentration. This results in delayed cell proliferation, reduced ATP, induction of autophagy, and dephosphorylation of the TORC1 substrates Atg13 and Sch9.

Effective treatment for suppression of acrylamide formation in fried potato chips using L-asparaginase from Bacillus subtilis

It has been reported that acrylamide, a potential carcinogen, is formed from the reaction of L-asparagine (L-Asn) and reducing sugars contained in foods during heating processes and free asparagine is a limiting factor for acrylamide formation. It has been reported that potato products such as potato chips, which are made through heating processes, contain high levels of acrylamide. To decrease the amount of L-Asn in potatoes using L-asparaginase, effective treatment conditions of sliced potatoes with the enzyme have been investigated. By treating sliced potatoes with Bacillus subtilis L-asparaginase II (BAsnase; 4 U/g potato), appriximately 40 % of L-Asn in the sliced potatoes was converted into L-aspartic acid (L-Asp). To make this enzyme more effective, prior to enzymatic treatment, sliced potatoes were freeze-thawed, dried at 90 °C for 20 min, and vacuum treated for 10 min under decompressed condition, resulting in the hydrolysis of approximately 90 % of L-Asn to L-Asp. The acrylamide content of BAsnase-treated fried potato chips decreased to below 20 % of that of BAsnase-untreated fried potato chips. Treatment conditions examined in this study were found to be effective to suppress the formation of acrylamide in fried potato chips.

Guidelines for the use and interpretation of assays for monitoring autophagy

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

Ksp1 kinase regulates autophagy via the target of rapamycin complex 1 (TORC1) pathway

Macroautophagy (hereafter autophagy) is a bulk degradation system conserved in all eukaryotes, which engulfs cytoplasmic components within double-membrane vesicles to allow their delivery to, and subsequent degradation within, the vacuole/lysosome. Autophagy activity is tightly regulated in response to the nutritional state of the cell and also to maintain organelle homeostasis. In nutrient-rich conditions, Tor kinase complex 1 (TORC1) is activated to inhibit autophagy, whereas inactivation of this complex in response to stress leads to autophagy induction; however, it is unclear how the activity of TORC1 is controlled to allow precise adjustments in autophagy activity. In this study, we performed genetic analyses in Saccharomyces cerevisiae to identify factors that regulate TORC1 activity. We determined that the Ksp1 kinase functions in part as a negative regulator of autophagy; deletion of KSP1 facilitated dephosphorylation of Atg13, a TORC1 substrate, which correlates with enhanced autophagy. These results suggest that Ksp1 down-regulates autophagy activity via the TORC1 pathway. The suppressive function of Ksp1 is partially activated by the Ras/cAMP-dependent protein kinase A (PKA), which is another negative regulator of autophagy. Our study therefore identifies Ksp1 as a new component that functions as part of the PKA and TORC1 signaling network to control the magnitude of autophagy.

Arthrobacter endo-beta-N-acetylglucosaminidase shows transglycosylation activity on complex-type N-glycan oxazolines: one-pot conversion of ribonuclease B to sialylated ribonuclease C

Asparagine-linked glycosylation is a major form of posttranslational modifications, which plays important roles in protein folding, intracellular signaling, and a number of other biological recognition events [1 ]. Glycoproteins are often characterized by their structural micro-heterogeneity where different glycoforms have the same polypeptide backbone but differ in the pendant oligosaccharides. Of particular interest are the findings that subtle difference in the attached glycans can have a significant impact on the biological functions of a given glycoprotein [2 , 3 ]. The urgent need of pure glycoforms for functional studies and biomedical applications has stimulated a great interest in exploring new methods for making homogeneous glycoproteins [4 ]. Major advances include the application of native chemical ligation and expressed protein ligation for constructing full-size glycoproteins [5 –7 ], chemoselective ligation to introduce homogeneous glycans [8 ], and the engineering of yeast glycosylation pathways to produce single glycoforms [9 ]. Yet another interesting advance in the field is the endoglycosidase-catalyzed transglycosylation for glycosylation engineering and glycoprotein synthesis [10 –16 ].

Glucosamine induces autophagy via an mTOR-independent pathway

Autophagy is a cellular process that nonspecifically degrades cytosolic components and is involved in many cellular responses. We found that amino sugars with a free amino group such as glucosamine, galactosamine and mannosamine induced autophagy via an mTOR-independent pathway. Glucosamine-induced autophagy at concentrations of at least 500 microM to over 40 mM. In the presence of 40 mM glucosamine, autophagy induction was initiated at 6h and reached a plateau at 36 h. Glucosamine-induced autophagy could remove accumulated ubiquitin-conjugated proteins as well as 79-glutamine repeats. Therefore, orally administered glucosamine could contribute to the prevention of neurodegenerative diseases and promotion of antiaging effects.

Efficient glycosynthase mutant derived from Mucor hiemalis endo-beta-N-acetylglucosaminidase capable of transferring oligosaccharide from both sugar oxazoline and natural N-glycan

Endo-M, an endo-beta-N-acetylglucosaminidase from Mucor hiemalis, is a family 85 glycoside hydrolase. This enzyme is unique in that it can transfer en bloc the oligosaccharide of various types of N-glycans onto different acceptors, and thereby it enzymatically generates diverse glycoconjugates. In this study, we performed mutational and kinetic studies focusing on a key catalytic asparagine 175 of Endo-M. We have shown that most of the Asn-175 mutants had significantly diminished hydrolysis activity but acted as glycosynthases capable of using synthetic sugar oxazoline for transglycosylation. Our results confirm the critical role of this asparagine residue in promoting the formation of an oxazolinium ion intermediate in the first step of the substrate-assisted catalysis. Interestingly, the N175Q mutant was found to possess dramatically enhanced glycosynthase-like activity with sugar oxazoline in comparison with N175A and a transglycosidase-like activity with "natural" N-glycan as well. These results also implicated the significance of amide side chain in the asparagine 175 of Endo-M for promoting oxazoline transglycosylation in the second step of the catalysis. The highly efficient syntheses of glycopeptides/glycoproteins by N175Q combined with synthetic sugar oxazolines or natural N-glycan substrates were exemplified. In addition, we also identified several previously unknown residues that seem to play a role in the catalysis of Endo-M.

Glycosynthases enable a highly efficient chemoenzymatic synthesis of N-glycoproteins carrying intact natural N-glycans

Homogeneous N-glycoproteins carrying defined natural N-glycans are essential for detailed structural and functional studies. The transglycosylation activity of the endo-beta-N-acetylglucosaminidases from Arthrobacter protophormiae (Endo-A) and Mucor hiemalis (Endo-M) holds great potential for glycoprotein synthesis, but the wild-type enzymes are not practical for making glycoproteins carrying native N-glycans because of their predominant activity for product hydrolysis. In this article, we report studies of two endoglycosidase-based glycosynthases, EndoM-N175A and EndoA-N171A, and their usefulness in constructing homogeneous N-glycoproteins carrying natural N-glycans. The oligosaccharide oxazoline corresponding to the biantennary complex-type N-glycan was synthesized and tested with the two glycosynthases. The EndoM-N175A mutant was able to efficiently transfer the complex-type glycan oxazoline to a GlcNAc peptide and GlcNAc-containing ribonuclease to form the corresponding homogeneous glycopeptide/glycoprotein. The EndoA-N171A mutant did not recognize the complex-type N-glycan oxazoline but could efficiently use the high-mannose-type glycan oxazoline for transglycosylation. These mutants possess the transglycosylation activity but lack the hydrolytic activity toward the product. Kinetic studies revealed that the dramatically enhanced synthetic efficiency of the EndoA-N171A mutant was due to the significantly reduced hydrolytic activity toward both the Man(9)GlcNAc oxazoline and the product as well as to its enhanced activity for transglycosylation. Thus, the two mutants described here represent the first endoglycosidase-based glycosynthases enabling a highly efficient synthesis of homogeneous natural N-glycoproteins.

Two thimet oligopeptidase-like Pz peptidases produced by a collagen-degrading thermophile, Geobacillus collagenovorans MO-1

A collagen-degrading thermophile, Geobacillus collagenovorans MO-1, was found to produce two metallopeptidases that hydrolyze the synthetic substrate 4-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-D-Arg (Pz-PLGPR), containing the collagen-specific sequence -Gly-Pro-X-. The peptidases, named Pz peptidases A and B, were purified to homogeneity and confirmed to hydrolyze collagen-derived oligopeptides but not collagen itself, indicating that Pz peptidases A and B contribute to collagen degradation in collaboration with a collagenolytic protease in G. collagenovorans MO-1. There were many similarities between Pz peptidases A and B in their catalytic properties; however, they had different molecular masses and shared no antigenic groups against the respective antibodies. Their primary structures clarified from the cloned genes showed lower identity (22%). From homology analysis for proteolytic enzymes in the database, the two Pz peptidases belong to the M3B family. In addition, Pz peptidases A and B shared high identities of over 70% with unassigned peptidases and oligopeptidase F-like peptidases of the M3B family, respectively. Those homologue proteins are putative in the genome database but form two distinct segments, including Pz peptidases A and B, in the phylogenic tree. Mammalian thimet oligopeptidases, which were previously thought to participate in collagen degradation and share catalytic identities with Pz peptidases, were found to have lower identities in the overall primary sequence with Pz peptidases A and B but a significant resemblance in the vicinity of the catalytic site.

Direct observation of charge transfer in double-perovskite-like RbMn[Fe(CN)6]

The charge density distribution has been determined for a transition metal cyanide, RbMn[Fe(CN)(6)], by means of the maximum entropy-Rietveld method combined with the highly angularly resolved synchrotron radiation x-ray powder diffraction at SPring-8 BL02B2. We directly observed a charge transfer from the Mn site to the Fe site in the low-temperature phase. On the basis of a local density approximation calculation, we discuss the origin for the anisotropic bonding electron distribution around the Mn3+ ion in the low-temperature phase.

Stichopus japonicus arginine kinase: gene structure and unique substrate recognition system

Arginine kinase from the sea cucumber Stichopus japonicus underwent a unique molecular evolution. Unlike the monomeric 40 kDa arginine kinases from molluscs and arthropods, Stichopus arginine kinase is dimeric, the same as cytoplasmic isoenzymes of the vertebrate creatine kinases. Its entire amino acid sequence is more similar to creatine kinases than to other arginine kinases, but the guanidino specificity region (GS region) is of the arginine kinase type. To elucidate its unusual evolution, the structure of the Stichopus arginine kinase gene was determined. It consisted of seven exons and six introns, and a part of the exon 2 of the Stichopus gene corresponds to the GS region. Compared with the structure of the human muscle creatine kinase gene (seven exons, six introns), the splice junctions of five introns were conserved exactly between the two genes, suggesting that these introns had been conserved for at least 500 million years. The entire sequence of Stichopus arginine kinase is distinctly included in the creatine kinase cluster in all tree construction methods examined. On the other hand, if the tree is constructed only from sequences corresponding to Stichopus exon 2, it is placed in the arginine kinase cluster. Thus we conclude that Stichopus arginine kinase evolved not from the arginine kinase gene but from the creatine kinase gene, and suggest that its GS region, determining substrate specificity, has been replaced by an arginine kinase type via exon shuffling. In typical arginine kinases four residues, Ser(63), Gly(64), Val(65) and Tyr(68) (numbering from the Limulus polyphemus sequence), in the GS region are highly conserved and are associated with substrate binding. Among them, Tyr(68) appears to play a crucial role by forming a hydrogen bond with the substrate, and is conserved exactly in all arginine kinases. However, in Stichopus arginine kinase, none of these four conserved residues were present. Nevertheless, the enzyme displays an affinity for the substrate arginine (K(m)=0.8 mM) comparable with other arginine kinases. This implies that a completely different substrate-binding system has been developed in Stichopus arginine kinase. We propose that the His(64) in Stichopus arginine kinase acts as a substitute for the Tyr(68) in other arginine kinases, and that the imidazole ring of His(64) is hydrogen bonded with the substrate arginine, thus stabilizing it.

Arginine kinase from Nautilus pompilius, a living fossil. Site-directed mutagenesis studies on the role of amino acid residues in the Guanidino specificity region

Arginine kinases were isolated from the cephalopods Nautilus pompilius, Octopus vulgaris, and Sepioteuthis lessoniana, and the cDNA-derived amino acid sequences have been determined. Although the origin and evolution of cephalopods have long been obscure, this work provides the first molecular evidence for the phylogenetic position of Cephalopoda in molluscan evolution. A crystal structure for Limulus arginine kinase showed that four amino acid residues (Ser(63), Gly(64), Val(65), and Tyr(68)) are hydrogen-bonded with the substrate arginine. We introduced three independent mutations, Ser(63) --> Gly, Ser(63) --> Thr, and Tyr(68) --> Ser, in Nautilus arginine kinase. One of the mutants had a considerably reduced substrate affinity, accompanied by a decreased V(max). In other mutants, the activity was lost almost completely. It is known that substantial conformational changes take place upon substrate binding in arginine kinase. We hypothesize that the hydrogen bond between Asp(62) and Arg(193) stabilizes the closed, substrate-bound state. Site-directed mutagenesis studies strongly support this hypothesis. The mutant (Asp(62) --> Gly or Arg(193) --> Gly), which destabilizes the maintenance of the closed state and/or perhaps disrupts the unique topology of the catalytic pocket, showed only a very weak activity (0.6-1.5% to the wild-type).

Evolution of phosphagen kinase VII. Isolation of glycocyamine kinase from the polychaete Neanthes diversicolor and the cDNA-derived amino acid sequences of alpha and beta chains

Glycocyamine kinase (GK) was isolated from the marine polychaete Neanthes diversicolor by gel filtration, DEAE-cellulose chromatography, butyl-Toyopearl hydrophobic chromatography, and chromatofocusing. The GK was eluted as a single peak on the latter three chromatographies, and the molecular mass for the native GK was estimated to be about 80 kDa. The SDS-PAGE showed that the isolated GK consists of two distinct subunits in equal proportion, alpha and beta chains, with molecular masses of 42.2 and 43.8 kDa, respectively. The present results suggest that the Neanthes GK has a heterodimeric structure. The cDNAs for alpha and beta chains of Neanthes GK were amplified by PCR and their cDNA-derived amino acid sequences were determined. The alpha and beta chains are composed of 374 and 390 amino acids, and the molecular masses were calculated to be 42,392 and 43,966 Da, respectively, in good agreement with the apparent masses on SDS PAGE. The beta chain has a characteristic N-terminal extension of 15 amino acids, and all of the sequence differences between alpha and beta chains were restricted in the N-terminal region of 50 residues. The overall sequence identity was 92%. The occurrence of heterodimeric nature in Neanthes GK is of great interest from the evolutionary point of view, because the heterodimeric structure is only known for creatine kinase MB-isozyme specific for mammalian heart muscle among phosphagen kinases.

Fine structure of SMG alginate fragment in the light of its degradation by alginate lyases of Pseudomonas sp

An alginate fragment named SMG, consisting of mannuronic (M) and guluronic acid residues (G)(DP=25), was prepared from the partial acid hydrolysate of a commercial alginate. Two subfractions, SMG-ppt (DP=52) and SMG-sup (DP=18) were obtained from SMG by fractionation with MgC12 and CaC12. The M/G ratios of these alginate fragment were 1.4-1.9. Their lysis products by a pseudomonad alginate lyase [EC 4.2.2.3] preparation were fractionated by gel filtration, giving similar patterns. The major products in their digests were unsaturated monouronides (53-50%) and triuronides (30-35%). The former was identified as a delta4,5-hexuronic acid (deltaU) and the latter was identified as a mixture of delta4,5-hexuronosyl-(1 leads to 4)-beta-D-mannuronosyl-(1 leads to 4)-L-guluronic acid (deltaUMG) and delta4,5-hexuronosyl-(1 leads to 4)-alpha-L-guluronosyl-(1 leads to 4))L-guluronic acid (deltaUGG). The two unsaturated triuronides were present in roughly equal amounts. The presence of 4-O-alpha-L-guluronosyl-L-guluronic acid (GG) and 4-O-beta-D-mannuronosyl-L-guluronic acid (MG) or 4-O-beta-L-guluronosyl-D-mannuronic acid (GM) was also demonstrated inthe digest. Moreover, indirect evidence suggested nonreducing terminal deltaU residue and free deltaU in the digest to be derived more from M than G of the original SMG. Thus, it was concluded that more than one-third of uronic acid residues of SMG molecules may be composed of almost equal amounts of MG and GG sequences, most of which may be connected by M to form MMG and MGG sequences, respectively.