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E L Malin

Publications and source records attributed to E L Malin.

13 recordsLinked to original sources
PubMed2005

Contributions of terminal peptides to the associative behavior of alphas1-casein.

The N- and C-terminal segments of bovine alphas1-casein-B (f1-23 and f136-196) were characterized under conditions that promoted or inhibited self-association to determine the relative contributions of each fragment to the interaction of alphas1-casein with itself or with other caseins. In earlier studies of f1-23, nuclear magnetic resonance (NMR) data and circular dichroism (CD) spectra showed that its conformation was thermostable between 10 degrees and 25 degrees C. In contrast, NMR studies of f136-196 indicated temperature sensitivity between 10 and 60 degrees C, as did near-UV and far-UV CD data, suggesting a molten globule-like structure at higher temperatures. To compare the effects of temperature on conformational attributes of alphas1-casein and its terminal peptides, additional CD studies were conducted over a broader temperature range (10 to 70 degrees C). The far-UV CD spectra indicated little temperature sensitivity for alphas1-casein, and the N-terminal peptide remained thermostable. During molecular dynamics simulations, the N-terminal peptide conformation did not change significantly, but the conformation of the C-terminal peptide (f136-196) was dramatically altered. These changes are correlated with the thermal instability observed by both CD and NMR in f136-196. Analytical ultracentrifugation studies of the self-association reactions of genetic variants A, B, and C of alphas1-casein showed that at 37 degrees C the associative state is primarily dimeric; the amounts of higher order polymers significantly decreased when temperature was increased from 20 to 37 degrees C. In all 3 genetic variants, the C-terminal portion of the whole molecule showed thermal instability with respect to aggregation to higher polymers, confirming the predictions of CD data and molecular dynamics simulations. The temperature dependency of these conformational changes suggests a possible function for alphas1-casein in facilitating casein-casein interactions in casein micelle formation.

Caseins↗
PubMed2001

Solution structures of casein peptides: NMR, FTIR, CD, and molecular modeling studies of alphas1-casein, 1-23.

To determine its potential for interacting with other components of the casein micelle, the N-terminal section of bovine alphas1-casein-B, residues 1-23, was investigated with nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopies, and molecular modeling. NMR data were not consistent with conventional alpha-helical or beta-sheet structures, but changes in N-H proton chemical shifts suggested thermostable structures. Both CD and FTIR predicted a range of secondary structures for the peptide (30-40% turns, 25-30% extended) that were highly stable from 5 degrees C to 25 degrees C. Other conformational elements, such as loops and polyproline II helix, were indicated by FTIR only. Molecular dynamics simulation of the peptide predicted 32% turns and 27% extended, in agreement with FTIR and CD predictions and consistent with NMR data. This information is interpreted in accord with recent spectroscopic evidence regarding the nature of unordered conformations, leading to a possible role of alphas1-casein (1-23) in facilitating casein-casein interactions.

Caseins↗
PubMed1992

Chromatographic and electrophoretic methods used for analysis of milk proteins.

Current knowledge of milk proteins and their behavior in dairy foods is based on early applications of chromatography and electrophoresis. Electrophoretic identification of the number and genetic variety of milk proteins inaugurated a research effort in which chromatographic techniques were successfully applied to the isolation of each milk protein, thus facilitating the characterization and further study of milk and dairy products. This review focuses on recent applications of chromatography for separations and analysis and on analytical applications of electrophoresis.

Chromatography↗
PubMed1992

Alkaline phosphatase in the lactating bovine mammary gland and the milk fat globule membrane. Release by phosphatidylinositol-specific phospholipase C.

1. Alkaline phosphatase is covalently bound to bovine mammary microsomal membranes and milk fat globule membranes through linkage to phosphatidylinositol as demonstrated by the release of alkaline phosphatase following treatment with phosphatidylinositol-specific phospholipase C. 2. The release of alkaline phosphatase from the pellet to the supernatant was demonstrated by enzyme assays and electrophoresis. 3. Electrophoresis of the solubilized enzymes showed that the alkaline phosphatase of the microsomal membranes contained several isozymes, while only one band with alkaline phosphatase activity was seen in the fat globule membrane. 4. Levamisole and homoarginine were potent inhibitors of the alkaline phosphatase activities in both membrane preparations and in bovine liver alkaline phosphatase, but not in calf intestinal alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1990

Differential release of proteins from bovine fat globule membrane.

Alkaline phosphatase and 5'-nucleotidase are covalently linked to phosphatidylinositol in bovine fat globule membrane, as demonstrated by their release following treatment with phospholipase C specific for phosphatidylinositol. The failure of this treatment to liberate phosphodiesterase I may indicate that it has a variant linkage resistant to release. In a test of exposure at the membrane surface, alkaline phosphatase and phosphodiesterase I, but not 5'-nucleotidase, were released from fat globule membrane by treatment with proteinase K. These apparent differences in accessibilities of membrane surface proteins suggest that attachment to phosphatidylinositol does not necessarily impart greater exposure to proteins with which it is linked.

5'-Nucleotidase↗
PubMed1989

Reactions of hydroxyamino acids during hydrochloric acid hydrolysis.

Chlorosubstitution reactions occur readily during HCl hydrolysis of delta- and epsilon-hydroxynorleucines (Hnle), the products of deamination of poly-L-lysine by nitrite at low pH. During amino acid analysis, chloronorleucines elute as new peaks after delta- and epsilon-Hnle. To determine if other hydroxyamino acids undergo similar changes during hydrolysis, they were subjected individually to HCl hydrolysis conditions with and without added phenol. Amino acid analyses indicated that terminal hydroxy groups on linear side chains undergo reactions during HCl hydrolysis; the products appear as new peaks which may be chloroderivatives. In contrast, no new peaks are observed in HCl hydrolysates of delta-hydroxylysine or amino acids with beta-hydroxy groups (beta-hydroxynorvaline, serine, and threonine). Phenol did not protect linear amino acids from reactions during HCl hydrolysis but did prevent loss of the cyclic amino acids tyrosine, hydroxyproline, and 3,4-dihydroxyphenylalanine. Although the gamma-hydroxy group of homoserine would be expected to undergo reaction, HCl catalyzes its cyclization to form homoserine lactone instead.

Amino Acids↗
PubMed1985

Spectrophotometric estimation of protein concentration in the presence of tryptophan modified by 2-hydroxy-5-nitrobenzyl bromide.

A spectrophotometric method makes it possible to determine the concentration of a protein after covalent modification of tryptophan residues by 2-hydroxy-5-nitrobenzyl bromide. Molar absorption coefficients for the 2-hydroxy-5-nitrobenzyl chromophore, reported here in the pH range from 4.0 to 10.9, can be used to correct the protein absorbance values at 280 nm, which then provides the basis for calculating protein concentration in the usual way. The method was tested with alpha-lactalbumin, beta-lactoglobulin, pepsin, and soybean trypsin inhibitor; spectrophotometrically estimated concentrations of these proteins agreed closely with values obtained by amino acid analysis.

2-Hydroxy-5-nitrobenzyl Bromide↗
PubMed1984

Separation and qualitative recovery of major proteins from a single sample of skeletal muscle.

The major soluble and myofibrillar proteins of skeletal muscle were separated into five fractions by extracting a single sample with solutions of increasing ionic strength and pH. After separation of myoglobin, other soluble proteins, and myosin, an acetone powder was prepared from the residue; the extractions were continued to yield actin and the troponin-tropomyosin complex. From 200 g of skeletal muscle the average recoveries were: total sarcoplasmic proteins, 4.5 g; myoglobin, 0.55 g; myosin, 2.7 g; actin, 0.1 g; and troponin-tropomyosin complex, 17.5 mg. The method was designed for investigating the effects of physical or chemical treatment of whole muscle or whole animals by monitoring changes in individual muscle proteins. This is particularly desirable for comparisons of amino acid composition, since naturally occurring levels of methylated histidine and lysine vary in vertebrate muscle among species, among individual members of a species, and among muscle types.

Actins↗
PubMed1980

Individual breathing reactions measured in hemoglobin by hydrogen exchange methods.

Protein hydrogen exchange is generally believed to register some aspects of internal protein dynamics, but the kind of motion at work is not clear. Experiments are being done to identify the determinants of protein hydrogen exchange and to distinguish between local unfolding and accessibility-penetration mechanisms. Results with small molecules, polynucleotides, and proteins demonstrate that solvent accessibility is by no means sufficient for fast exchange. H-exchange slowing is quite generally connected with intramolecular H-bonding, and the exchange process depends pivotally on transient H-bond cleavage. At least in alpha-helical structures, the cooperative aspect of H-bond cleavage must be expressed in local unfolding reactions. Results obtained by use of a difference hydrogen exchange method appear to provide a direct measurement of transient, cooperative, local unfolding reactions in hemoglobin. The reality of these supposed coherent breathing units is being tested by using the difference H-exchange approach to tritium label the units one at a time and then attempting to locate the tritium by fragmenting the protein, separating the fragments, and testing them for label. Early results demonstrate the feasibility of this approach.

Deuterium↗