Structural components of alginic acid. I. The crystalline structure of poly-beta-D-mannuronic acid. Results of x-ray diffraction and polarized infrared studies

A Structure determination of the naturally occuring marine algal polysaccharide poly-β-D -mannuronic acid is described. The structure consists of 1e → 4e linked D -mannuronic acid chains with the monosaccharide units in the C1 chair conformation. The X-ray fiber diffraction photograph obtained from bundles of fibers prepared from Fucus vesiculosus has been indexed to an orthorhombic unit cell in which a =7.6 Å, b (fiber axis) = 10.4 Å, c = 8.6 Å, the unit cell containing two disaccharide chain segments with space group P2₁2₁2₁. A sheet-like structure involving one intra-chain, one intra-sheet, and one inter-sheet hydrogen bond per monosaccharide is proposed. Features of the chain-packing arrangement are compared with mannan.     

Kinetic Analysis of the Noncompetitive Inhibition of the Lignin-Peroxidase-catalyzed Reaction by Oxalic Acid

Oxalic acid was found to inhibit noncompetitively the Cα-Cβ bond cleavage of veratrylglycerol catalyzed by a lignin peroxidase (LiP) isozyme of the white-rot fungus P. chrysosporium. With greater amounts of oxalic acid in the LiP system, the substrate was not converted to veratraldehyde but was almost all recovered. Oxalic acid was shown to be decomposed to CO₂ during the enzymatic reaction. The results clearly indicate that oxalic acid reduced the cation radical intermediate formed in the reaction back to the substrate to block the production of veratraldehyde. A novel equation has been derived to explain the mechanism for this unique non-competitive inhibition that is different from the classical noncompetitive one. The inhibition constant K_i obtained here, which is different from the classical inhibition constant K_i, is defined as the ratio of the rate constant (k_p) for product formation to the rate constant (k_i) for the reduction of the cation radical to the substrate.     

Volatile C6-Aldehyde Formation via Hydroperoxides from C18-Unsaturated Fatty Acids in Etiolated Alfalfa and Cucumber Seedlings

1. Etiolated seedlings of alfalfa and cucumber evolved n-hexanal from linoleic acid and cis-3-hexenal and trans-2-hexenal from linolenic acid when they were homogenized.

2. The activities for n-hexanal formation from linoleic acid, lipoxygenase and hydro-peroxide lyase were maximum in dry seeds and 1~2 day-old etiolated seedlings of alfalfa, and in 6~7 day-old etiolated seedlings of cucumber.

3. n-Hexanal was produced from linoleic acid and 13-hydroperoxylinoleic acid by the crude extracts of etiolated alfalfa and cucumber seedlings. cis-3-Hexenal and trans-2-hexenal were produced from linolenic acid and 13-hydroperoxylinolenic acid by the crude extracts of etiolated alfalfa and cucumber seedlings. But these extracts, particulariy cucumber one, showed a high isomerizing activity from cis-3-hexenal to trans-2-hexenal.

4. When the C₈-aldehydes were produced from linoleic acid and linolenic acid by the crude extracts, formation of hydroperoxides of these C₁₈-fatty acids was observed.

5. When 9-hydroperoxylinoleic acid was used as a substrate, trans-2-nonenal was produced by the cucumber homogenate but not by the alfalfa homogenate.

6. As the enzymes concerned with C₆-aldehyde formation, lipoxygenase was partially purified from alfalfa and cucumber seedlings and hydroperoxide lyase, from cucumber seedlings. Lipoxygenase was found in a soluble fraction, but hydroperoxide lyase was in a membrane bound form. Alfalfa lipoxygenase catalyzed formation of 9- and 13-hydroperoxylinoleic acid (35: 65) from linoleic acid and cucumber one, mainly 13-hydroperoxylinoleic acid formation. Alfalfa hydroperoxide lyase catalyzed n-hexanal formation from 13-hydroperoxylinoleic acid, but cucumber one catalyzed formation of n-hexanal and trans-2-nonenal from 13- and 9-hydroperoxylinoleic acid, respectively.

7. From the above results, the biosynthetic pathway for C₆-aldehyde formation in etiolated alfalfa and cucumber seedlings is established that C₆-aldehydes (n-hexanal, cis-3-hexenal and trans-2-hexenal) are produced from linoleic acid and linolenic acid via their 13-hydroperoxides by lipoxygenase and hydroperoxide lyase.     

Squishy lipids: Temperature effects on the betaine and galactolipid profiles of a C18/C18 peridinin‐containing dinoflagellate,Symbiodinium microadriaticum (Dinophyceae), isolated from the mangrove jellyfish,Cassiopea xamachana

Previous work from our laboratory has shown dinoflagellates, which possess the carotenoid peridinin, have been divided into two clusters based on plastid galactolipid fatty acid composition. In one cluster major forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), lipids that comprise the majority of photosynthetic membranes, were C₁₈/C₁₈ (sn‐1/sn‐2), with octadecapentaenoic [18:5(n‐3)] and octadecatetraenoic [18:4(n‐3)] acid as principal fatty acids. The other cluster contained C₂₀/C₁₈ major forms, with eicosapentaenoic acid [20:5(n‐3)] being the predominant sn‐1 fatty acid. In this study, we have found that Symbiodinium microadriaticum isolated from the jellyfish, Cassiopea xamachana, when grown at 30°C, produced MGDG and DGDG with a more saturated fatty acid, 18:4(n‐3), at the sn‐2 carbon than when grown at 20°C where 18:5(n‐3) predominates. This modulation of the sn‐2 fatty acid's level of saturation is mechanistically similar to what has been observed in Pyrocystis, a C₂₀/C₁₈ dinoflagellate. We have also examined the effect of growth temperature on the betaine lipid, diacylglycerylcarboxyhydroxymethylcholine (DGCC), which has been observed by others to be the predominant non plastidial polar lipid in dinoflagellates. Temperature effects on it were minimal, with very few modulations in fatty acid unsaturation as observed in MGDG and DGDG. Rather, the primary difference seen at the two growth temperatures was the alteration of the amount of minor forms of DGCC, as well as a second betaine lipid, diacylglyceryl‐N,N,N‐trimethylhomoserine.     

Neutral amino acid transport by marine fish intestine: role of the side chain

This work was devoted to the study of the structure-affinity relationships in neutral amino acid transport by intestinal brush border of marine fish (Dicentrarchus labrax). The effects of the length of the side chain on kinetics of glycine, alanine, methionine and amino isobutyric acid were investigated. In the presence of K⁺ two components were characterized: one is saturable by increased substrate concentrations, whereas the other can be described by simple diffusion mechanism. Simple diffusion, a passive, non-saturable, Na⁺-independent route, contributes largely to the transport of methionine and to a much lesser extend to alanine, glycine or alphaaminoisobutyric acid uptakes. If a branched chain is present, as in the case of amino isobutyric acid, diffusion is low. A Na⁺-independent, saturable system has been fully characterized for methionine, but not for branched amino acids such as amino isobutyric acid. In the presence of Na⁺ saturable components were shown. Two distinct Na⁺-dependent pathways have been characterized for glycine uptake, with low and high affinities. For alanine and methionine only one Na⁺-dependent high affinity system exists with the same half-saturation concentration and the same maximum uptake at saturable concentrations. Glycine high affinity system has the same half-saturation concentration as methionine or alanine uptake, whereas maximum uptake is lower. The substitution of the hydrogen by a methyl group results in a severe decrease of uptake (aminoisobutyric acid). Mutual inhibition experiments indicate that the same carriers could be responsible for methionine and alanine uptakes and probably glycine Na⁺-dependent uptake. The influence of Na⁺ concentrations (100^-1 mol·l^-1) on amino acid uptake was examined. Glycine, alanine, methionine and amino isobutyric acid transport can be described by a hyperbolic function, with a saturation uptake which is highly increased for methionine. However, the half-saturation concentration does not seem to be strongly affected by the amino acid structure. The effect of Na⁺ concentration (25 and 100 mmol·l^-1) on the kinetics of methionine uptake have been also examined. The maximum uptake of the saturable system clearly shows a typical relationship with concentration.Abbreviations [AA] amino acid concentration - AIB aminoisobutyric acid - [I] Inhibitor amino acid concentration - J _i uptake in the presence of inhibitor - J _o uptake without inhibitor - K _d passive diffusion constant - K _i inhibitor constant - K _t concentration of test amino acid for half-maximal flux - MES 2[N-morpholino]ethanesulphonic acid - V _max maximum uptake at saturable amino acid concentrations - V _tot total amino acid uptake     

Enzyme inhibition by p-cresol and lacticacid in lipase-mediated synthesis of p-cresyl acetate and stearoyl lactic acid: a kinetic study

A detailed kinetic study was carried out to investigate the porcine pancreatic lipase-catalysed esterification reactions of p-cresol–acetic acid and lactic acid–stearic acid. The kinetic data were in agreement with a Ping Pong Bi–Bi mechanism being followed by the enzyme, where inhibition is indicated in the presence of p-cresol and lactic acid in the respective reactions. Mathematical analyses of experimentally observed initial rates yielded various kinetic parameters, K _m(p-cresol) = 0.1, K _{m(acetic acid)} = 0.54, K _{m(lactic acid)} = 0.059 M, K _{m(stearic acid)} = 0.04 M, V _{max(p-cresol–acetic acid)} = 13.2(h^–1), V _{max(lactic acid–stearic acid)} = 0.00163 M/h, K _i(p-cresol) = 0.59 and K _{i(lactic acid)} = 0.079 M. The K _m and K _i values of p-cresol and lactic acid observed in the respective reactions showed both the competitive nature of binding between the substrates p-cresol and acetic acid on the one hand and lactic acid and stearic acid on the other and the inhibitory nature of p-cresol and lactic acid.     

A Hypothetical Cyclic Pathway for the Metabolism of Odd-carbon n-Alkanes or Propionyl-CoA via Seven-carbon Tricarboxylic Acids in Yeasts

An extensive study has been undertaken to elucidate the physiological significance of threo-D_s-2-methylisocitric acid produced mainly from odd-carbon n-alkanes by a mutant strain of Candida lipolytica. The mutant strain showed slower growth responses to odd-carbon n-alkanes, especially of shorter chain-length, and failed to utilize this acid as sole carbon source, whereas the parent strain and many other yeasts tested were able to utilize this acid. About one half of yeasts tested accumulated this acid extracellularly. Under a thiamine-deficient condition, amounts of pyruvate produced by the parent strain from odd-carbon n-alkanes were ten times as large as those from even-carbon n-alkanes. A scheme for the partial oxidation of propionyl-CoA to pyruvate via C₇-tricarboxylic acid by yeasts was supposed. This scheme may offer suggestion on the metabolism of propionyl-CoA by other living organisms. A hypothetical pathway of citrate accumulation from odd-carbon n-alkane was also presented.     

Etude “in vitro” des acides gras synthétisés dans les microsomes de cerveaux de souris normales et “quaking”

Radiogas chromatographic studies of the products of fatty acid biosynthesis in mice brain microsomes confirm the existence of a «de novo system from acetyl-CoA and malonyl-CoA and of a least two elongating systems for long chain fatty acids, involving malonyl-CoA. The possibility of an intermediary system leading from C₁₈ to C₂₀ fatty acids has been evoked.Comparison between non mutant and quaking mice indicates that all the microsomal fatty acid biosynthetic systems are depressed. The biosynthetic system elongating fatty acids from C₁₈ is the one which is the most modified quantitatively and qualitatively in quaking. Microsomal and soluble «de novo systems are qualitatively intact.     

Isolation of Allo-isoleucic Acid (α-Hydroxy-β-methylvaleric Acid) and β-Hydroxy-β-methylvaleric Acid from Turkish Tobacco Leaves

A new method determining the activity of tannin acyl hydrolase (tannase) was made. This method was based on the change in optical density of substrate tannic acid at 310 mμ. In this method, the error of measurement was about 1~3%, and many samples could be tested at one time because of its simplicity.

The procedure was as follows; To four parts of substrate (0.350 w/v% of tannic acid dissolved in 0.05m citrate buffer, pH 5.5), one part of the enzyme solution was added.

After t minutes reaction at 30°C, 0.1 part of the mixture was added to ten parts of 90% ethanol.

The optical density of the ethanol solution at 310 mμ was measured. Tannase activity (unit/ml) was given by following equation. $u=114\times \frac{E_{t1}?E_{t2}}{t_2?t_1}$

Where E_t1 and E_t2 mean the optical density of the ethanol solution at 310 mμ prepared after t₁ and t₂ minutes reaction, and one unit of the enzyme means the amount of the enzyme which is able to hydrolyze one μ mole of the ester bond in tannic acid in one minute.

The substrate tannic acid used in this determining method was purified. It was composed of one mole of glucose and nine moles of gallic acid, and eight moles of which formed four moles of m-digallic acid.     

Analysis of the sensing and transducing processes implicated in the stomatal responses to carbon dioxide in Commelina communis L.

It has been previously debated whether CO₂ would depolarize the guard cell plasma membrane through malate‐mediated activation of the anion channel. Moreover, it has been assessed that the CO₂ signal would be transduced via cytosolic free Ca^{2 +} . In the present study, the CO₂ sensing and transducing processes were reinvestigated in Commelina communis (L.) mainly by studying how L ‐(–)‐malic acid and Ca^{2 +} flux modulators affected different CO₂ stomatal responses. L ‐(–)‐malic acid (1 m M ) inhibited by about 50% both CO₂‐induced stomatal closing and CO₂‐triggered inhibition of the stomatal opening response to the auxin indolyl‐3‐butyric acid. Stomatal closing in response to atmospheric CO₂ was strongly inhibited by the 1,4 dihydropyridines SDZ‐202 791 R(–) (SDZ (–)) and nifedipine, and this inhibition was attenuated by the 1,4 dihydropyridines SDZ‐202 791 S( + ) and S‐(–)‐BAY K8644. Suboptimal concentrations of the slow anion channel blockers 5‐nitro‐2,3‐phenylpropyllamine benzoic acid and anthracene‐9‐carboxylic acid increased the 50% inhibition of the CO₂ closing response by the Ca^{2 +} flux modulators SDZ (–) and 1,2‐bis(o‐aminophenoxy)ethane‐N,N,N ′ N ′ ‐tetraacetic acid in a stronger manner than an additive one. Together, these results support the view that CO₂ is sensed through reducing proton extrusion. Moreover, they might suggest that the CO₂ signal is transduced through Ca^{2 +} signalling arising from depolarization‐mediated activation of a putative plasma membrane voltage‐gated L‐type Ca^{2 +} channel and for which the plasma membrane slow anion channel is a potential target.     

KINETICS OF AMINO ACID INFLUX INTO NITELLA FLEXILIS1

The uptake of amino acids by Nitella flexilis has been investigated. Influx of glycine, alanine, and valine appears to be a diffusive process. Influx ranged from 0.14 to 0.06 and 0.04 pmoles/(cm)(sec), respectively. Aspartic acid uptake is an active transport mechanism. The V_max is 2.8 pmoles/(cm)(sec); the transport constant (Michaelis constant) K_m, 7.8 × 10^?3 M. The uptake of arginine is apparently due to 2 transport systems, one with a V_max and K_m of 3.1 pmoles/(cm)(sec) and 3.2 × 10^?3M, respectively. The second system has a V_max of 1.4 pmoles/(cm)(sec) and a K_m of 2.1 × 10^?4 M. The possibility that the second system is diffusive has been considered.     

Effect of Trace Levels of Nigericin on Intracellular pH and Acid-Base Transport in Rat Renal Mesangial Cells

Nigericin is an ionophore commonly used at the end of experiments to calibrate intracellularly trapped pH-sensitive dyes. In the present study, we explore the possibility that residual nigericin from dye calibration in one experiment might interfere with intracellular pH (pH _i ) changes in the next. Using the pH-sensitive fluorescent dye 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF), we measured pH _i in cultured rat renal mesangial cells. Nigericin contamination caused: (i) an increase in acid loading during the pH _i decrease elicited by removing extracellular Na⁺, (ii) an increase in acid extrusion during the pH _i increase caused by elevating extracellular [K⁺], and (iii) an acid shift in the pH _i dependence of the background intracellular acid loading unmasked by inhibiting Na-H exchange with ethylisopropylamiloride (EIPA). However, contamination had no effect on the pH _i dependence of Na-H exchange, computed by adding the pH _i dependencies of total acid extrusion and background acid loading. Nigericin contamination can be conveniently minimized by using a separate line to deliver nigericin to the cells, and by briefly washing the tubing with ethanol and water after each experiment. Received: 14 October 1998/Revised: 2 March 1999     

Biochemical characterization of anArabidopsis glucosyltransferase with high activity toward Jasmonic acid

Biochemical characterization of the recombinant gene products from theArabidopsis glucosyltransferase multigene family has identified one enzyme with high activity toward the plant cellular regulator jasmonic acid (JA). The protein, AtJGT1 (UDP-glucose:JA glucosyltransferase), also has significant activities with other substrates, such as dihydrojasmonicacid, indole-3-acetic acid (IAA), indole-3-propionic acid, and indole-3-butyric acid. TheK _M values of AtJGT1 for JA or IAA are similar to those of anArabidopsis IAA glucosyltransferase UGT84B1 previously reported. Northern blot analysis showed thatAtJGTI is highly expressed in the leaves, but only slightly detectable in the roots, stems, and inflorescences. This study describes the first biochemical analysis of a recombinant glucosyltransferase with JA activity, and provides the foundation for future genetic approaches to understanding the role of JA-glucose inArabidopsis.     

trans-Stilbene degradation by Arthrobacter sp. SL3 cells

trans-Stilbene degradation was examined by the reaction using resting cells of microorganisms isolated through the enrichment culture using trans-stilbene. The strain SL3, showing the highest trans-stilbene-degrading activity, was identified as Arthrobacter sp. One of the reaction products was identified to be cis,cis-muconic acid. Arthrobacter sp. SL3 cells also transformed benzaldehyde, benzoic acid and catechol into cis,cis-muconic acid, suggesting that one benzene ring of trans-stilbene was converted into cis,cis-muconic acid via benzaldehyde formed by its C_α=C_β bond cleavage.     

KINETICS OF COMPETITIVE INHIBITION OF NEUTRAL AMINO ACID TRANSPORT ACROSS THE BLOOD-BRAIN BARRIER

The transport of tryptophan across the blood-brain barrier is used as a specific example of a general approach by which rates of amino acid influx into brain may be predicted from existing concentrations of amino acids in plasma. The kinetics of inhibition of [¹⁴C]tryptophan transport by four natural neutral amino acids (phenylalanine, leucine, methionine, and valine) and one synthetic amino acid (α-methyl tyrosine) is studied with a tissue-sampling, single injection technique in the barbiturate-anesthetized rat. The equality of the K₁ (determined from cross-inhibition studies) and the K_m (determined from auto-inhibition data) for neutral amino acid transport indicate that these amino acids compete for a single transport site in accordance with the kinetics of competitive inhibition. Based on equations derived for competitive inhibition, apparent K_m values are computed for the essential neutral amino acids from known data on amino acid transport K_m and plasma concentrations. The apparent K_m values make possible predictions of the in vivo rates of amino acid influx into brain based on given plasma amino acid concentrations. Finally, a method is presented for determining transport constants from saturation data obtained with single injection techniques.     

Novel metabolic routes during the oxidation of hydroxylated aromatic acids by the yeast Arxula adeninivorans

Aim: To complete our study on tannin degradation via gallic acid by the biotechnologically interesting yeast Arxula adeninivorans as well as to characterize new degradation pathways of hydroxylated aromatic acids. Methods and Results: With glucose‐grown cells of A. adeninivorans, transformation experiments with hydroxylated derivatives of benzoic acid were carried out. The 12 metabolites were analysed and identified by high performance liquid chromatography and GC/MS. The yeast is able to transform the derivatives by oxidative and nonoxidative decarboxylation as well as by methoxylation. The products of nonoxidative decarboxylation of protocatechuate and gallic acid are substrates for further ring fission. Conclusion: Whereas other organisms use only one route of transformation, A. adeninivorans is able to carry out three different pathways (oxidative, nonoxidative decarboxylation and methoxylation) on one hydroxylated aromatic acid. The determination of the K_M‐values for protocatechuate and gallic acid in crude extracts of cells of A. adeninivorans cultivated with protocatechuate and gallic acid, respectively, suggests that the decarboxylation of protocatechuate and gallic acid may be catalysed by the same enzyme. Significance and Impact of the Study: This transformation pathway of protocatechuate and gallic acid via nonoxidative decarboxylation up to ring fission is novel and has not been described so far. This is also the first report of nonoxidative decarboxylation of gallic acid by a eukaryotic micro‐organism.     

The distribution of fatty acids including petroselinic and tariric acids in the fruit and seed oils of the Pittosporaceae, Araliaceae, Umbelliferae, Simarubaceae and Rutaceae

The fatty acid composition of the fruit oils or seed oils of Pittosporaceae (eight genera, 10 species), Araliaceae (two species), Simarubaceae (three species), and of one umbelliferous and one rutaceous species were determined by gas chromatography, argentation TLC and ozonolysis. In the Pittosporaceae, in which the major C₁₈ fatty acid of all species was either oleic acid (18:1, 9c) or linoleic acid (18:2, 9c, 12c), large amounts of C₂₀ and C₂₂ fatty acids seem to occur regularly. Petroselinic (18:1, 6c) and tariric (18:1, 6a) acids were absent. However, petroselinic acid was the major fatty acid in the Araliaceae and Umbelliferae. In these two families only small amounts of C₂₀ and C₂₂ acids were detected and tariric acid was absent. The Rutales contained relatively high amounts of trans-octadecenoic acids (18:1, 9t). Tariric acid was the major fatty acid in the two species of Picramnia (Simarubraceae), which also contained small amounts of petroselinic acid. The major fatty acids in Ailanthus glandulosa (Simarubaceae) and Phellodendron amurense (Rutaceae) were linoleic or linolenic acid (18:3, 9c, 12c, 15c); these species contained neither tariric nor petroselinic acid and the levels of C₂₀ and C₂₂ fatty acids were low. The appearance of schizogenous resin canals and polyacetylenes and the absence of iridoids and petroselinic acid allows the Pittosporaceae to be separated from the Rutales and Araliales and to be placed in an independent order, the Pittosporales. Arguments for a rather close relationship of the Pittosporales to the Araliales and Cornales (including the Escalloniaceae) are presented.     

Inhibition of C4 photosynthesis by (benzamidooxy)acetic acid

(Benzamidooxy)acetic acid (common name benzadox) which has herbicidal properties was evaluated as a potential inhibitor of photosynthesis in C₄ plants. Among enzymes of the C₄ pathway, it was a relatively strong inhibitor of alanine aminotransferase in in vitro experiments at concentrations of 5mM. In benzadox treated leaves of Panicum miliaceum, a NAD-malic enzyme type C₄ species, there was strong inhibition of both alanine and aspartate aminotransferase and of photosynthetic O₂ evolution within one hour. Consistent with the inhibition of these enzymes of the C₄ cycle, the pool sizes of metabolites of the cycle was altered: the aspartate level was increased two fold, while the levels of other metabolites such as pyruvate, alanine, oxalacetate and malate were decreased. Kinetic studies with partially purified alanine aminotransferase showed that benzadox is a competitive inhibitor with respect to alanine and a noncompetitive inhibitor with respect to 2-oxoglutarate. Comparisons between the structures and inhibitory actions of benzadox and (aminooxy)acetic acid, the latter a potent inhibitor of alanine and aspartate aminotransferases, suggest that in vivo, benzadox may exert its effect through metabolism to (aminooxy)acetic acid.Abbreviations benzadox (benzamidooxy)acetic acid - DTE dithioerythritol This research was supported in part by gift funds from Monsanto Agricultural Products Company. St. Louis, Missouri, and by NSF Grant PCM-8107953.     

A computer system for the analysis of molecular evolution modes of protein-encoding genes (SAMEM): The relationship between molecular evolution and phenotypic traits

An online computer system for the analysis of the molecular evolution modes of genes and proteins has been developed (SAMEM: ). SAMEM computations are based on the ratio of radical to conservative amino acid substitutions (K _R /K _C ), the rate of amino acid substitutions in the course of protein evolution (V _P ), and statistical relationships between the evolutionary changes of all known amino acid properties and particular features of an organism. The system facilitates the interpretation of the results of K _R /K _C and V _P analyses.     

Cloning and characterization of a gene encoding ABP57, a soluble auxin-binding protein

Auxin-binding protein 57 (ABP₅₇), a soluble auxin-binding protein, acts as a receptor to activate plasma membrane (PM) H⁺-ATPase. Here, we report the cloning of abp57 and the biochemical characterization of its protein expressed in E. coli. The analysis of internal amino acid sequences of ABP₅₇ purified from rice shoots enabled us to search for the corresponding gene in protein DB of NCBI. Further BLAST analysis showed that rice has four abp57-like genes and maize has at least one homolog. Interestingly, Arabidopsis seems to have no homolog. Recombinant ABP₅₇ expressed in E. coli caused the activation of PM H⁺-ATPase regardless of the existence of IAA. Scatchard analysis showed that the recombinant protein has relatively low affinity to IAA as compared to natural ABP₅₇. These results collectively support the notion that the cloned gene is responsible for ABP₅₇.