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O Markovic

Publications and source records attributed to O Markovic.

11 recordsLinked to original sources
PubMed1992

Disulfide bridges in tomato pectinesterase: variations from pectinesterases of other species; conservation of possible active site segments.

Analysis of tomato pectinesterase by carboxymethylation, with and without reduction, shows that the enzyme has two intrachain disulfide bridges. Analysis of fragments obtained from the native enzyme after digestion with pepsin identified bridges connecting Cys-98 with Cys-125, and Cys-166 with Cys-200. The locations of disulfide bridges in tomato pectinesterase are not identical to those in three distantly related pectinesterases (18-33% residue identities) from microorganisms. However, one half-Cys (i.e., Cys-166) position is conserved in all four enzymes. Sequence comparisons of the overall structures suggest a special importance for three short segments of the entire protein. One segment is at the N-terminal part of the tomato pectinesterase, another in the C-terminal portion near the distal end of the second disulfide loop, and the third segment is located in the central part between the two disulfide bridges. The latter segment, encompassing only 40 residues of the entire protein, appears to high-light a functional site in a midchain segment.

Amino Acid Sequence↗
PubMed1992

Antiserum to prolactin decreases rapid eye movement sleep (REM sleep) in the male rat.

Previous reports suggest that blood-born prolactin (PRL) may selectively promote rapid eye movement sleep (REMS). To study the possible involvement of endogenous PRL in sleep regulation, rats were systemically injected with either antiserum to PRL or normal rabbit serum, and the sleep-wake activity was determined during the subsequent 12-h light cycle. The administration of normal rabbit serum in physiological saline did not alter sleep-wake activity compared to control recordings, whereas the PRL antiserum caused a modest and selective suppression in REMS. Immunoreactive PRL was eliminated from the serial plasma samples obtained between 6 to 11 h after the injection of the antiserum. Brain temperature was not affected by the antiserum. The results indicate that physiological pituitary PRL secretion has a slight REMS-promoting activity in the male rat. It is speculated that an increased release of pituitary PRL or the PRL-like substance previously demonstrated in the brain may significantly stimulate REMS.

Animals↗
PubMed1990

Tomato and Aspergillus niger pectinesterases. Correlation of differences in existing reports: large species variations.

Existing reports on the enzyme tomato pectinesterase differ in alignments of two internal segments and in many single-residue replacements. The alignment from cDNA data, with a 317-residue mature protein, is correct, but protein analyses also show at least 18 single-residue replacements, suggesting the presence of many native or (less likely) cloning-derived microheterogeneities. Purification of Aspergillus niger pectinesterase and N-terminal sequence analysis of this enzyme reveal a different structure and indicate an extensive protein divergence.

Amino Acid Sequence↗
PubMed1988

A new chromogenic substrate for assay and detection of alpha-amylase.

A new soluble chromogenic substrate for alpha-amylase was prepared by coupling partially hydrolyzed starch with a dye, Ostazin brilliant red H-3B. The substrate is precipitable from buffered solutions with ethanol and is equally suitable for assay of alpha-amylase, detection of separated alpha-amylase isoenzymes in gels, and selection of microbial producers of the enzyme.

Chromogenic Compounds↗
PubMed1986

Pectinesterase. The primary structure of the tomato enzyme.

The first primary structure of a pectinesterase has been determined by analysis of the main form of this plant enzyme from tomatoes. The analysis was untraditional in the sense that few data were obtained by frequently used methods. Thus, digestion with trypsin, Glu-specific protease and several other enzymes gave limited cleavages and highly insoluble products. Instead, the determination was to a large extent based on peptides derived from chemical cleavages with CNBr at Met, N-chlorosuccinimide at Trp and hydroxylamine at Asn-Gly, plus an enzymatic cleavage at modified cysteine residues after chemical derivatizations. The structure shows the protein chain to be 305 residues long, with four half-cystine residues and five tryptophan residues. The N-terminus has a free alpha-amino group (from isoleucine). Two types of residue, tyrosine and histidine, have been functionally implied in the catalytic activity of the enzyme. Tyrosine is common in the protein (at 18 positions). However, only two histidine residues are found, and both are close to tyrosine residues in the primary structure (His-128 separated by one intervening residue from Tyr-126, and His-269 adjacent to Tyr-268), defining segment(s) of possible interest in relation to the active site.

Amino Acid Sequence↗
PubMed1985

Sensitive detection of endo-1,4-beta-glucanases and endo-1,4-beta-xylanases in gels.

A simple, highly sensitive zymogram technique for detection of endo-1,4-beta-glucanases and endo-1,4-beta-xylanases in polyacrylamide gels after electrophoresis or isoelectric focusing was developed. The detection employs transparent agar replicas containing soluble covalently dyed polysaccharides, hydroxyethylcellulose dyed with Ostazin brilliant red H-3B and beechwood 4-O-methyl-D-glucurono-D-xylan dyed with Remazol brilliant blue R, as the respective substrates. The high sensitivity of the detection is achieved by selective removal of depolymerized dyed substrates from the agar replicas by solvents which neither solubilize nor precipitate the original nondegraded dyed polysaccharides present in the agar gel.

Aspergillus niger↗
PubMed1977

Enzyme kinetics in single cells: concept and model.

We describe a technique whereby it is possible to measure enzyme activity in a singel cell. The model chosen involved the measurement of myeloperoxidase activity in a polymorphonuclear neutrophil leukocyte. Details of the apparatus are described. The experiments necessary to optimize the reaction conditions are summarized. The nature of the phases of the reaction are described. The technique appears to have further application in measurement of the activities of other enzymes in leukocytes or other cells.

Densitometry↗
PubMed1976

Pectic enzymes.

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Bacteria↗