Isolation and properties of four alpha-amylase isozymes from human submandibular saliva

Salivary proteome and its genetic polymorphisms

Salivary diagnostics for oral as well as systemic diseases is dependent on the identification of biomolecules reflecting a characteristic change in presence, absence, composition, or structure of saliva components found under healthy conditions. Most of the biomarkers suitable for diagnostics comprise proteins and peptides. The usefulness of salivary proteins for diagnostics requires the recognition of typical features, which make saliva as a body fluid unique. Salivary secretions reflect a degree of redundancy displayed by extensive polymorphisms forming families for each of the major salivary proteins. The structural differences among these polymorphic isoforms range from distinct to subtle, which may in some cases not even affect the mass of different family members. To facilitate the use of modern state-of-the-art proteomics and the development of nanotechnology-based analytical approaches in the field of diagnostics, the salient features of the major salivary protein families are reviewed at the molecular level. Knowledge of the structure and function of salivary gland-derived proteins/peptides has a critical impact on the rapid and correct identification of biomarkers, whether they originate from exocrine or non-exocrine sources.

Two forms of α-amylase in mantle tissue of Mytilus galloprovincialis: Purification and molecular properties of form II

alpha-Amylase activity has been shown for the first time in a non-digestive tissue from Mytilus galloprovincialis. alpha-amylase from mussel mantle tissue has been purified by affinity chromatography on insoluble starch, followed by gel-filtration chromatography on Superdex-200. The chromatographic and electrophoretic behaviour of M. galloprovincialis alpha-amylase and stability characteristics suggest two forms of this enzyme: one form forming stable aggregates (form I) and a monomeric form (form II) that is more abundant, active and unstable. Both forms show an inverse quantitative variation. Purified form II was highly unstable and the molecular mass was estimated to be 66 kDa by sodium dodecyl sulphate (SDS)-gel electrophoresis. Maximum activity was noted at pH 6.5 and 35 degrees C.

Patterns of secretion of mucins and non-mucin glycoproteins in human submandibular/sublingual secretion

The present investigation has characterised the influence of gustatory stimulation and duration of stimulation on the secretion pattern of salivary mucins MG1 and MG2 and non-mucin glycoproteins in submandibular/sublingual secretion (SMSL). Resting SMSL was collected for three 2 min intervals and stimulated SMSL was collected for ten 1 min intervals from six healthy subjects. Flow rates and total protein were significantly different under the two conditions. The secretion patterns of these proteins under resting and stimulated conditions was examined on periodic acid-Schiff reagent (PAS)-stained polyacrylamide gels using a Kodak Digital-Science Image Station. Image analyses revealed that the level of MG1 increased and the level of MG2 remained nearly the same after stimulation. Six other major glycoproteins (designated Band 1-6) were identified on the basis of their electrophoretic mobilities and immuno-reactivity on Western blots. After stimulation the intensity of Band 1 (lactoferrin and peroxidase) and Band 2 (amylase) decreased whereas the intensity of Band 3 (carbonic anhydrase), Band 4 (proline-rich glycoprotein) and Bands 5 and 6 (basic glycosylated proline-rich proteins) increased. These patterns probably reflect secretion from preformed vesicles since de novo synthesis would be unexpected within the time frame of these experiments. The variable patterns observed suggest that mucins and non-mucin glycoproteins in SMSL derive from different subsets of secretory vesicles, some of which may originate in mucous and others in serous acini, as well as in ductal cells. Quantification of mucins was performed by image analysis technology using purified MG1 and MG2 standards. Finally, the present investigation has shown that the secretory patterns of mucins and non-mucin glycoproteins from submandibular/sublingual glands are complex and represent an important aspect of salivary gland physiology.

Slow-binding inhibition of branching enzyme by the pseudooligosaccharide BAY e4609

Branching enzyme from Escherichia coli is shown to be inhibited by the pseudooligosaccharide BAY e4609. The mechanism of binding is studied in detail by kinetics using reduced amylose as substrate. Lineweaver-Burk plots suggest the mechanism of a noncompetitive or slow-binding inhibitor. Further studies by progress curves and rate of loss of branching activity allows us to conclude BAY e4609 as being a slow-binding inhibitor of branching enzyme. We discuss how these results parallel the inhibition of alpha-amylase by acarbose and the significance of branching enzyme as belonging to the amylolytic family.

Human salivary mucin MG1 selectively forms heterotypic complexes with amylase, proline-rich proteins, statherin, and histatins

Heterotypic complexes between the high-molecular-weight mucin MG1 and other salivary proteins in human submandibular/sublingual secretion (HSMSL) could have a significant impact on the biological properties of these proteins in oral fluids in both health and disease. We describe a mild procedure for isolation and purification of native MG1 by gel filtration chromatography on Sepharose CL-2B which does not involve dialysis, lyophilization, use of denaturing agents, or covalent modification. Western blots of native MG1 probed with antibodies against 8 different salivary proteins showed that complexing occurs between MG1 and salivary amylase, proline-rich proteins (PRPs), statherins, and histatins but not MG1, sIgA, secretory component, or cystatins. When native MG1 was placed in 4 M guanidine hydrochloride and chromatographed on Sepharose CL-4B, ELISA measurement of column fractions showed that amylase, PRPs, statherins, and histatins were released. Interestingly, gel filtration resolved the material which eluted into 4 or 5 distinct peaks, suggesting that the released entities were heterotypic complexes. From these studies, the occurrence of at least three different types of complexes between MG1 and other salivary proteins has been identified. Type 1 complexes are dissociated by SDS-PAGE and in 4 M guanidine hydrochloride. Type II complexes are not dissociated under these conditions. Type III complexes are dissociated during SDS-PAGE and by 4 M guanidine hydrochloride, but the released proteins appear to be complexes containing amylase, PRPs, statherins, and histatins. The possible functional role of heterotypic complexes between MG1 and other salivary proteins as a physiologic delivery system, a mechanism for protection against proteolysis, a repository for precursors of the acquired enamel pellicle, and a vehicle for modulation of the viscoelastic and rheological properties of saliva is discussed.

Hydrolases acting on glycosidic bonds: chromatographic and electrophoretic separations

We describe analyses of unusual human alpha-amylase, performed in our laboratory and review available methods for amylase study. Electrophoretic and chromatographic methods provide an effective means for the analysis of amylase isoenzymes and unusual amylase. The recent identification of a selective inhibitor and a monoclonal antibody to amylase isoenzyme contributes to rapid routine clinical assays of amylase isoenzymes. However unusual amylases such as variants, macroamylasemia and sialyl salivary-type amylasemia cannot be detected by those conventional methods. The unusual amylases can only be detected by electrophoresis and can be easily characterized by combination study with chromatographic methods. Electrophoretic and chromatographic methods are universal means to validate unusual amylases found in patient sera. Further basal studies are needed to define the roles of salivary amylase in exocrine fluids using those separation techniques.

A contemporary view of salivary research

The past 50 years of salivary research has been marked by a series of changing perceptions as new techniques and technologies have illuminated the complexities of the secretory mechanism, salivary composition, and function. The modern era began with the innovations of electrophoresis, chromatography, histochemistry, immunochemistry, electron microscopy, and microphysiology. The idea of saliva as primarily a digestive fluid composed of salts, amylase, and mucin was rapidly broadened to encompass a wide spectrum of protective proteins with the dual responsibility of protecting both hard and soft tissues. Characterization of the secretory IgA and nonimmunological antibacterial systems and the proteins responsible for the regulation of calcium and phosphate levels dominated the research in the 1960s and 1970s. An appreciation of the nature, formation, and role of the salivary pellicle and the interplay between bacterial adherence and agglutination provided a clinical thrust. Morphologists and physiologists redefined the secretory process on a molecular level. The 1980s saw the union of structure and function, both in terms of synthesis and release of the secretory products and their specific roles in the oral cavity in health and disease. The excitement of the 1990s is in the genetic control of processes and products, elucidating the mechanisms, and using the information to improve on nature: an era of great expectations and hubris. This article is essentially a personal guided tour through the past 50 years of salivary research.

Electrophoretic characterization of posttranslational modifications of human parotid salivary alpha-amylase

Human salivary alpha-amylase displays multiple bands upon native polyacrylamide gel electrophoresis. In fresh saliva, due to posttranslational modifications, a pattern of 5-6 isozymes is observed. The isozymes are designated 1-6, in the order of increasing anodal mobility. As a result of the development of a rapid and sensitive electrophoresis system, with markedly higher resolution than previously reported, we concluded that a previously proposed model (Karn et al., Biochem. Genet. 1973, 10, 341-350) is inadequate to explain the origin of the various bands. We propose an alternative model that fits in with our new and previously made observations. According to this model, band 2 is the primary gene product and band 1 is its glycosylated counterpart--with only one neutral oligosaccharide present on each molecule. Band 3 originates from band 1 by the transialidase-catalyzed incorporation of sialic acid into the biantennary chain. Bands 4 and 6 originate from bands 2 and 4, respectively, by deamidation; band 5 is the deamidation product of amylase with an acidic oligosaccharide (band 3). Only a minor part of band 3 consists of the deamidation product of band 1. Peptide Asn-Gly-Ser (residues 427-429) is the most probable candidate for glycosylation; literature data suggests that deamidation occurs in the stretch Glu-Asn-Gly-Lys-Asp (residues 364-368) and Asn-Gly-Asn-Cys (residues 474-477). Both glycosylation and deamidation might play a role in the clearance of amylase from the systemic circulation. The electrophoresis system described is a powerful tool to determine amylase isozyme distributions in health and disease, especially for the screening of alterations seen in ectopically produced amylase.

Purification of lingual amylase from serous glands of rat tongue and characterization of rat lingual amylase and lingual lipase

Lingual amylase and lingual lipase, two digestive enzymes that are secreted from lingual serous glands (von Ebner's), were simultaneously purified from rat lingual serous glands with hydrophobic chromatography used as the final step. This method, previously developed for the purification of lingual lipase, includes homogenization of rat lingual serous glands, 100,000 g centrifugation, ammonium sulfate precipitation of proteins, and extraction of lipids with acetone at -20 degrees C, followed by hydrophobic chromatography on ethyl agarose or Agethane. Amylase was eluted after the elution of proteins that did not interact with the hydrophobic gel at pH 6.3. Lingual lipase was eluted with a solution containing micelles of taurodeoxycholate, monoolein, and oleic acid. Analysis of each of the purified enzymes by SDS-polyacrylamide gel electrophoresis revealed one band at Mr = 59,000 for amylase and one band at Mr = 51,000 for lingual lipase. Isoelectric focusing of amylase indicated a strong band at pI = 5.0 and two very faint bands at pI = 4.9 and 4.8, possibly isozymes or deamidated protein. Amino acid and hexosamine analyses were performed on the enzymes after electroelution from SDS-polyacrylamide gels. Both lingual lipase and lingual amylase had a high content of dicarboxylic (free and amide) amino acids. For lingual lipase and lingual amylase, the % molar ratios of aspartic acid/asparagine were 15.35 and 15.10, and the % molar ratios of glutamic acid/glutamine were 7.07 and 7.20, respectively. Lingual amylase was very similar to rat parotid, pancreatic, and mouse salivary amylases, except that it contained more proline (11.03% molar ratio).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of molecular weight of native proteins by polyacrylamide gradient gel electrophoresis

An improved method for the estimation of molecular weights of native proteins by polyacrylamide gel electrophoresis, in 9 cm x 9 cm x 0.05 mm 4-20% T fabric reinforced gradient gels, is described. Plotting the logarithm of the relative mobilities of proteins versus gel concentrations produces lines whose slopes are related to molecular weights.

Expression of the human salivary alpha-amylase gene in yeast and characterization of the secreted protein

Recombinant plasmids were constructed in which the human salivary alpha-amylase gene, with or without the N-terminal signal sequence for secretion, was placed under control of the APase (PHO5) promoter of Saccharomyces cerevisiae. In yeast cells transformed with the alpha-amylase gene having the human signal sequence for secretion, the gene was expressed and the enzyme was secreted into the medium in three different glycosylated forms. The amylase gene without the signal sequence was also expressed in yeast, but the products were neither secreted nor glycosylated. Determination of the N-terminal amino acid (aa) sequence revealed that the 15-aa signal sequence had been cleaved from the secreted enzyme, and that the N-terminal residue, glutamine, had been modified into pyroglutamate, as is commonly observed with the mammalian salivary alpha-amylase. Thus, the human salivary alpha-amylase signal sequence for secretion was correctly recognized and processed by the yeast secretory pathway. The C-terminal residue was identified as leucine, which is predicted from the nucleotide sequence data to be located at position 511 in front of the termination codon. Therefore, there is no post-translational processing in formation of the C terminus.

Biochemistry of human alpha amylase isoenzymes

The purpose of this article is to review recent literature on the isoenzymes of alpha amylase. Although some studies are cited from the literature of fields other than clinical biochemistry, the aim is to bring together findings that may be of interest to clinical laboratory physicians and scientists. It is hoped that this will be useful in suggesting further studies of amylase. To this end, the review is more selective than exhaustive. The review will discuss the history and chemistry alpha amylases, the measurement of amylase and amylase isoenzymes, posttranslational modifications of human amylases, and the genetics of human pancreatic and salivary amylases. Finally, we will discuss other tissue sources of amylase with emphasis on "genital" amylases and their relationship to the amylase found in serous ovarian tumors.

Radioimmunoassay of human salivary amylase: cross-reactivity with human and porcine pancreatic amylase and other salivary proteins

A radioimmunoassay (RIA) of human salivary amylase was developed. Human salivary and pancreatic amylases were purified by Sephacryl S-200 gel filtration and by cation-exchange chromatography. Human salivary amylase antibody, raised in New Zealand white rabbits, did not crossreact with other salivary proteins and there was also no crossreactivity with purified porcine pancreatic amylase. The antibody crossreacted with human pancreatic amylase to the extent of 25%. Amylase concentrations, estimated by RIA, in human saliva, serum, and urine were compared with enzymatic activity. Correlation of results obtained by the two techniques was best for estimation of amylase in saliva, least for serum and intermediate for urine. Amylase concentrations and enzymatic activity in stimulated parotid saliva were not correlated with flow rate of secretion. There was no correlation between amylase concentrations (and enzymatic activity) in parotid saliva and those found either in serum and urine. Amylase comprises approximately 5% of the total parotid salivary protein in humans.

Glomerular charge alterations in human minimal change nephropathy

A theoretical model of charge and size selectivity for the glomerulus has been applied to human data. Using previously published values for GFR, renal plasma flow, systemic oncotic pressure, and fractional clearances of neutral dextrans, albumin, salivary amylase, and transferrin, membrane parameters describing the glomerular barrier were determined for normal individuals under control conditions and during lysine infusion (which retards tubule protein reabsorption), and for patients with minimal change nephropathy (MCN). To permit the estimation of membrane charge from fractional clearances, molecular charge values for human transferrin (-9.4 Eq/mole) and human salivary amylase (-4.1) were determined by measuring electrophoretic mobilities of these proteins in polyacrylamide gels. Assuming no large changes in the transmural hydraulic pressure difference (delta P), the glomerular ultrafiltration coefficient (Kf, the product of hydraulic permeability and capillary surface area) was calculated to be reduced by greater than 50% in MCN. The effective pore radius (approximately 55 A) is virtually unaltered in MCN, suggesting that the decline in Kf is due to a reduced number of pores. The degree of albuminuria observed in MCN is attributable to an approximately 50% reduction in the concentration of fixed negative charges in the glomerular capillary wall. The concentrations of fixed charges calculated from albumin data in normal individuals (140 to 160 mEq/liter) and in patients with MCN (60 to 90 mEq/liter) are insensitive to the assumed values of delta P.

Characterization of cysteine-containing phosphoproteins from human submandibular-sublingual saliva

Members of a family of acidic proteins taken from human submandibular-sublingual saliva were designated cysteine-containing phosphoproteins, since they could be distinguished from other salivary phosphoproteins by the presence of half-cystine. These molecules consisted of a single peptide chain of approximately 14,000 daltons. Their isoelectric points ranged from 4.3 to 5.9. Two groups (C2 and C3) were O-phosphorylated. Their charge heterogeneity was apparently due to variations in content of phosphate and acidic and basic amino acids.