1
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van Boven A, Konings WN. A Phosphate-Bond-Driven Dipeptide Transport System in Streptococcus cremoris Is Regulated by the Internal pH. Appl Environ Microbiol 2010; 53:2897-902. [PMID: 16347504 PMCID: PMC204219 DOI: 10.1128/aem.53.12.2897-2902.1987] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The uptake of amino acids and peptides by Streptococcus cremoris is mediated by different highly specific transport systems. The leucine transport system has a high affinity only for leucine, isoleucine, and valine and no affinity for leucyl-peptides. The transport system for leucyl-leucine is strongly inhibited by several dipeptides with hydrophobic, neutral, N-terminal amino acids but not by leucine. The leucyl-leucine transport system has a high affinity for dipeptides containing beta-methyl groups in the side chain; the C terminus of the dipeptide affects the affinity to a much lower extent. Leucyl-leucine transport in whole cells was studied as a function of the internal pH at different external pH values in the presence and absence of nigericin. The internal pH was shown to be an important controlling factor in leucyl-leucine uptake, but the DeltapH was not involved as a driving force. At increasing external pH values, the affinity of the transport system for leucyl-leucine decreased. Uptake of leucyl-leucine was also studied in the presence of arsenate, which inhibited ATP synthesis by substrate-level phosphorylation. The rate of leucyl-leucine transport appeared to be dependent on the intracellular ATP concentrations. These results indicate that the energy for the leucyl-leucine transport is directly supplied by ATP.
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Affiliation(s)
- A van Boven
- Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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2
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Abstract
SummaryThe present study identifies proline-specific peptidases found inStreptococcus cremorisAM2. These activities were present prcdominantly in the cytoplasmic fraction of the cells with minor amounts in cell membrane fraction. No evidence vvas found for such activities in either the extracellular fluid used to grow the cells, in the wash fraction or in the cell wall fraction. The involvement of these enzymes in release of free proline from proline-containing peptides is considered.
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3
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Prolidase activity of Lactococcus lactis subsp. cremoris AM2: partial purification and characterization. J DAIRY RES 2009. [DOI: 10.1017/s0022029900026868] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SummaryProlidase activity from cytoplasm of Lactococcus lactis subsp. cremoris (Streptococcus cremoris) AM2 was partially purified. The enzyme had Mr 42000 and optimum activity between pH 7·35 and 8·25 in citrate, phosphate and borate buffers while in a universal buffer system an optimum pH between 8·3 and 9·0 was observed. The activity was strongly inhibited by the chelating agents E.DTA, 1,10-phenanthroline and 8-hydroxyquinoline. Inhibition was also noted with dithio-threitol, N-ethylmaleimide and bacitracin. The enzyme was active on all amino-acylproline substrates tested except Gly-Pro and Gip-Pro and also showed activity against Pro-Pro. While most prolyl amino acids tested were not hydrolysed, hydrolysis was noted with Pro-Ala and Pro-Val. Km values of 20 mM and 10 mM were obtained with Phe-Pro and Met-Pro respectively; however, substrate inhibition was observed with Ile-Pro and Leu-Pro.
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4
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Abstract
SummarySeveral strains ofLactococcus lactissubsp.lactis, Lactobacillus caseiandLactobacillus plantarumisolated from traditional goats' cheese have been studied for titratable acidity, proteolysis in milk and enzymic activities. Aminopeptidasc activities were measured with whole cells and cells permeabilized with Triton X-100. Caseinolytic activity was investigated using electrophoresis in polyacrylamide gel with sodium dodecyl sulphate.Lc. lactissubsp.lactishad a level of proteolytic activity in skim milk greater than that ofLb. casei, while this activity inLb. plantarumwas very low. Alanine aminopeptidase activity was almost non-existent for all strains tested, while lysine aminopeptidase activity appeared to be of fundamentally intracellular origin. Leucine aminopeptidase activity was also greater in cells that had been permeabilized than in whole cells forLb. caseiandLb. plantarum. Lc. lactissubsp.lactisleucine aminopeptidase activity was greater in whole cells. No significant hydrolysis of casein was found withLb. caseiI FPL 725 andLb. plantarumIFPL 722 permeabilized with Triton X-100 after 24 h incubation with whole bovine casein.
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5
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Rimpiläinen MA, Niskasaari K, Juutinen KMS, Nurmiaho-Lassila EL, Forsean RI. The plasma membrane ofStreptococcus cremoris:isolation and partial characterization. ACTA ACUST UNITED AC 2008. [DOI: 10.1111/j.1365-2672.1986.tb05083.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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6
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Choi H, Laleye L, Amantea G, Simard R. Production of Aminopeptidase from Skim Milk Whey Permeate Medium by Lactobacillus casei ssp. casei. J Dairy Sci 1996. [DOI: 10.3168/jds.s0022-0302(96)76446-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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7
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Farkye NY, Madkor SA, Atkins HG. Proteolytic abilities of some lactic acid bacteria in a model cheese system. Int Dairy J 1995. [DOI: 10.1016/0958-6946(95)00032-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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8
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Isolation and purification of cell wall-associated arginine carboxypeptidase fromStreptococcus mitis ATCC 15909. Curr Microbiol 1994. [DOI: 10.1007/bf01569053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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9
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Crow VL, Holland R, Pritchard GG, Coolbear T. The diversity of potential cheese ripening characteristics of lactic acid starter bacteria: 2. The levels and subcellular distributions of peptidase and esterase activities. Int Dairy J 1994. [DOI: 10.1016/0958-6946(94)90004-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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10
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Castro MAM, Mart�n-Hern�ndez MC. Determination of aminopeptidase activity in cheese. Eur Food Res Technol 1994. [DOI: 10.1007/bf01195276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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11
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Characterization of growth and enzymes produced by prt+lac+ and prt-lac-Lactococcus lactis cells. Appl Biochem Biotechnol 1993. [DOI: 10.1007/bf02918995] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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12
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Pritchard GG, Coolbear T. The physiology and biochemistry of the proteolytic system in lactic acid bacteria. FEMS Microbiol Rev 1993; 12:179-206. [PMID: 8398214 DOI: 10.1111/j.1574-6976.1993.tb00018.x] [Citation(s) in RCA: 210] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The inability of lactic acid bacteria to synthesize many of the amino acids required for protein synthesis necessitates the active functioning of a proteolytic system in those environments where protein constitutes the main nitrogen source. Biochemical and genetic analysis of the pathway by which exogenous proteins supply essential amino acids for growth has been one of the most actively investigated aspects of the metabolism of lactic acid bacteria especially in those species which are of importance in the dairy industry, such as the lactococci. Much information has now been accumulated on individual components of the proteolytic pathway in lactococci, namely, the cell envelope proteinase(s), a range of peptidases and the amino acid and peptide transport systems of the cell membrane. Possible models of the proteolytic system in lactococci can be proposed but there are still many unresolved questions concerning the operation of the pathway in vivo. This review will examine current knowledge and outstanding problems regarding the proteolytic system in lactococci and also the extent to which the lactococcal system provides a model for understanding proteolysis in other groups of lactic acid bacteria.
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Affiliation(s)
- G G Pritchard
- Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand
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13
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Sahlstrøm S, Chrzanowska J, Sørhaug T. Purification and characterization of a cell wall peptidase from Lactococcus lactis subsp. cremoris IMN-C12. Appl Environ Microbiol 1993; 59:3076-82. [PMID: 8215377 PMCID: PMC182409 DOI: 10.1128/aem.59.9.3076-3082.1993] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A peptidase from the cell wall fraction of Lactococcus lactis subsp. cremoris IMN-C12 has been purified to homogeneity by hydrophobic interaction chromatography, two steps of anion-exchange chromatography, and gel filtration. The molecular mass of the purified enzyme was estimated to be 72 kDa by gel filtration and 23 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme has a pI of 4.0, and it has the following N-terminal sequence from the 2nd to the 17th amino acid residues: -Arg-Leu-Arg-Arg-Leu-?-Val-Pro-Gly-Glu-Ileu-Val-Glu-Glu-Leu-Leu. The peptidase is most active at pH 5.8 and at 33 degrees C with trileucine as the substrate. Reducing agents such as dithiothreitol, beta-mercaptoethanol, and cysteine strongly stimulated enzyme activity, while p-chloromercuribenzoate had an inhibitory effect. Also, metal chelators lowered the peptidase activity, which could not be restored with Ca2+ and Mg2+. The divalent cations Cu2+, Zn2+, Fe2+, and Hg2+ completely inhibited peptidase activity. The peptidase is capable of hydrolyzing tripeptides and some dipeptides, with a preference for peptides containing leucine and with the highest activity towards the tripeptides Leu-Leu-Leu, Leu-Trp-Leu, and Ala-Leu-Leu, which were hydrolyzed with Kms of 0.37, 0.18, and 0.61 mM, respectively.
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Affiliation(s)
- S Sahlstrøm
- Department of Dairy and Food Industries, Agricultural University of Norway, As
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14
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Affiliation(s)
- P S Tan
- Department of Microbiology, University of Groningen, Haren, The Netherlands
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15
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16
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Bacon CL, Wilkinson M, Vincent Jennings P, Ni Fhaolain I, O'Cuinn G. Purification and characterisation of an aminotripeptidase from cytoplasm of Lactococcus lactis subsp. cremoris AM2. Int Dairy J 1993. [DOI: 10.1016/0958-6946(93)90015-r] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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17
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Baankreis R, Exterkate FA. Characterisation of a Peptidase from Lactococcus lactis ssp* cremoris HP that Hydrolyses Di- and Tripeptides Containing Proline or Hydrophobic Residues as the Aminoterminal Amino Acid. Syst Appl Microbiol 1991. [DOI: 10.1016/s0723-2020(11)80305-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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18
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Bockelmann W, Fobker M, Teuber M. Purification and characterization of the X-prolyl-dipeptidyl-aminopeptidase from Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus acidophilus. Int Dairy J 1991. [DOI: 10.1016/0958-6946(91)90027-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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19
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20
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Abstract
The proteolytic system of lactic acid bacteria is of eminent importance for the rapid growth of these organisms in protein-rich media. The combined action of proteinases and peptidases provides the cell with small peptides and essential amino acids. The amino acids and peptides thus liberated have to be translocated across the cytoplasmic membrane. To that purpose, the cell contains specific transport proteins. The internalized peptides are further degraded to amino acids by intracellular peptidases. The world-wide economic importance of the lactic acid bacteria and their proteolytic system has led to an intensive research effort in this area and a considerable amount of biochemical data has been collected during the last two decades. Since the development of systems to genetically manipulate lactic acid bacteria, data on the genetics of enzymes and processes involved in proteolysis are rapidly being generated. In this review an overview of the latest genetic data on the proteolytic system of lactic acid bacteria will be presented. As most of the work in this field has been done with lactococci, the emphasis will, inevitably, be on this group of organisms. Where possible, links will be made with other species of lactic acid bacteria.
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Affiliation(s)
- J Kok
- Department of Genetics, University of Groningen, Haren, The Netherlands
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21
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22
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Tan PS, Konings WN. Purification and Characterization of an Aminopeptidase from
Lactococcus lactis
subsp.
cremoris
Wg2. Appl Environ Microbiol 1990; 56:526-32. [PMID: 16348128 PMCID: PMC183372 DOI: 10.1128/aem.56.2.526-532.1990] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
An aminopeptidase was purified to homogeneity from a crude cell extract of
Lactococcus lactis
subsp.
cremoris
Wg2 by a procedure that included diethyl-aminoethane-Sephacel chromatography, phenyl-Sepharose chromatography, gel filtration, and high-performance liquid chromatography over an anion-exchange column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 95,000. The aminopeptidase was capable of degrading several peptides by hydrolysis of the N-terminal amino acid. The peptidase had no endopeptidase or carboxypeptidase activity. The aminopeptidase activity was optimal at pH 7 and 40�C. The enzyme was completely inactivated by the
p
-chloromecuribenzoate mersalyl, chelating agents, and the divalent cations Cu
2+
and Cd
2+
. The activity that was lost by treatment with the sulfhydryl-blocking reagents was restored with dithiothreitol or β-mercapto-ethanol, while Zn
2+
or Co
2+
restored the activity of the 1,10-phenantroline-treated enzyme. Kinetic studies indicated that the enzyme has a relatively low affinity for lysyl-
p
-nitroanilide (
K
m
, 0.55 mM) but that it can hydrolyze this substrate at a high rate (
V
max
, 30 μmol/min per mg of protein).
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Affiliation(s)
- P S Tan
- Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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23
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Abu-Tarboush H, Marshall R, Heymann H. Peptides Produced by Selected Lactose-Positive and Lactose-Negative Lactococci in a Model Cheese Ripening System. J Dairy Sci 1989. [DOI: 10.3168/jds.s0022-0302(89)79472-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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24
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Neviani E, Boquien CY, Monnet V, Thanh LP, Gripon JC. Purification and Characterization of an Aminopeptidase from
Lactococcus lactis
subsp.
cremoris
AM2. Appl Environ Microbiol 1989; 55:2308-14. [PMID: 16348010 PMCID: PMC203073 DOI: 10.1128/aem.55.9.2308-2314.1989] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
An aminopeptidase was purified from cell extracts of
Lactococcus lactis
subsp.
cremoris
AM2 by ion-exchange chromatography. After electrophoresis of the purified enzyme in the presence or absence of sodium dodecyl sulfate, one protein band was detected. The enzyme was a 300-kilodalton hexamer composed of identical subunits not linked by disulfide bridges. Activity was optimal at 40°C and pH 7 and was inhibited by classical thiol group inhibitors. The aminopeptidase hydrolyzed naphthylamide-substituted amino acids, as well as dipeptides and tripeptides. Longer protein chains such as the B chain of insulin were hydrolyzed, but at a much slower rate. The Michaelis constant (
K
m
) and the maximal rate of hydrolysis (
V
max
) were, respectively, 4.5 mM and 3,600 pkat/mg for the substrate
l
-histidyl-β-naphthylamide. Amino acid analysis showed that the enzyme contained low levels of hydrophobic residues. The partial N-terminal sequence of the first 19 residues of the mature enzyme was determined. Polyclonal antibodies were obtained from the purified enzyme, and after immunoblotting, there was no cross-reaction between these antibodies and other proteins in the crude extract.
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Affiliation(s)
- E Neviani
- Station de Recherches Laitières, Institut National de la Recherche Agronomique, 78350 Jouy-en-Josas, Laboratoire de Génie des Procédés Biotechnologiques Agro-alimentaires, Institut National de la Recherche Agronomique, 78850 Thiverval-Grignon, and Station de Pathologie Porcine et d'Immunologie, Institut National de la Recherche Agronomique, Nouzilly, 37380 Monnaie, France
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25
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Kamaly KM, Marth EH. Enzyme Activities of Lactic Streptococci and Their Role in Maturation of Cheese: A Review. J Dairy Sci 1989. [DOI: 10.3168/jds.s0022-0302(89)79318-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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26
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Sahlström S, Espinosa C, Langsrud T, Sørhaug T. Cell Wall, Membrane, and Intracellular Peptidase Activities of Propionibacterium shermanii. J Dairy Sci 1989. [DOI: 10.3168/jds.s0022-0302(89)79115-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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27
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Smid EJ, Driessen AJ, Konings WN. Mechanism and energetics of dipeptide transport in membrane vesicles of Lactococcus lactis. J Bacteriol 1989; 171:292-8. [PMID: 2492499 PMCID: PMC209585 DOI: 10.1128/jb.171.1.292-298.1989] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Alanyl-alpha-glutamate transport has been studied in Lactococcus lactis ML3 cells and in membrane vesicles fused with liposomes containing beefheart cytochrome c oxidase as a proton-motive-force-generating system. The uptake of Ala-Glu observed in de-energized cells can be stimulated 26-fold upon addition of lactose. No intracellular dipeptide pool could be detected in intact cells. In fused membranes, a 40-fold accumulation of Ala-Glu was observed in response to a proton motive force. Addition of ionophores and uncouplers resulted in a rapid efflux of the accumulated dipeptide, indicating that Ala-Glu accumulation is directly coupled to the proton motive force as a driving force. Ala-Glu uptake is an electrogenic process and the dipeptide is transported in symport with two protons. In both fused membranes and intact cells the same affinity constant (0.70 mM) for Ala-Glu uptake was found. Accumulated Ala-Glu is exchangeable with externally added alanyl-glutamate, glutamyl-glutamate, and leucyl-leucine, while no exchange occurred upon addition of the amino acid glutamate or alanine. These results indicate that the Ala-Glu transport system has a broad substrate specificity.
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Affiliation(s)
- E J Smid
- Department of Microbiology, University of Groningen, Haren, The Netherlands
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28
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Kamaly KM, Marth EH. Proteinase and Peptidase Activities of Cell-Free Extracts from Mutant Strains of Lactic Streptococci. J Dairy Sci 1988. [DOI: 10.3168/jds.s0022-0302(88)79818-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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29
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30
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van Boven A, Tan PST, Konings WN. Purification and Characterization of a Dipeptidase from
Streptococcus cremoris
Wg2. Appl Environ Microbiol 1988; 54:43-49. [PMID: 16347537 PMCID: PMC202394 DOI: 10.1128/aem.54.1.43-49.1988] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A dipeptidase was purified to homogeneity from a crude cell extract of
Streptococcus cremoris
Wg2 by DEAE-Sephacel column chromatography followed by preparative disc gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 49,000. The dipeptidase is capable of hydrolyzing a range of dipeptides, but not peptides with longer chains. The enzyme was shown to be a metallo-Mn
2+
enzyme with a pH optimum of 8 and a temperature optimum of 50�C. The enzyme is strongly inhibited by thiol-reducing reagents but not by sulfhydryl reagents. Kinetic studies indicated that the enzyme has a relatively low affinity for leucyl-leucine and alanyl-alanine (
K
m
, 1.6 and 7.9 mM, respectively) but can hydrolyze these substrates at very high rates (
V
max
, 3,700 and 13,000 μmol/min per mg of protein, respectively).
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Affiliation(s)
- A van Boven
- Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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31
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32
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Exterkate FA, de Veer GJ. Purification and Some Properties of a Membrane-Bound Aminopeptidase A from
Streptococcus cremoris. Appl Environ Microbiol 1987; 53:577-83. [PMID: 16347306 PMCID: PMC203709 DOI: 10.1128/aem.53.3.577-583.1987] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A membrane-bound
l
-α-glutamyl (aspartyl)-peptide hydrolase (aminopeptidase A) (EC 3.4.11.7) from
Streptococcus cremoris
HP has been purified to homogeneity. The free γ-carboxyl group rather than the amino group of the N-terminal
l
-α-glutamyl (aspartyl) residue appeared to be essential for catalysis. No endopeptidase activity could be established with this enzyme. The native enzyme is a polymeric, most probably trimeric, metalloenzyme (relative molecular weight, approximately 130,000) which shows on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels apparent high relative molecular weight values due to (lipid?) material dissociable with butanol. The subunit (relative molecular weight, approximately 43,000) is catalytically inactive. The enzyme is inactivated completely by dithiothreitol, chelating agents, and the bivalent metal ions Cu
2+
and Hg
2+
. Of the sulfhydryl-blocking reagents tested, only
p
-hydroxymercuribenzoate appeared to inhibit the enzyme. Activity lost by treatment with a chelating agent could be restored by Co
2+
and Zn
2+
. The importance of the occurrence of an aminopeptidase A in
S. cremoris
with respect to growth in milk is discussed.
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Affiliation(s)
- F A Exterkate
- Netherlands Institute for Dairy Research, 6710 BA Ede, The Netherlands
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