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L Sirakov

Publications and source records attributed to L Sirakov.

At least 19 recordsLinked to original sources
PubMed1999

Essential metal ions alter the lactoferrin binding to the erythrocyte plasma membrane receptors.

The effect of metal ions at a concentration of 10(-8) to 10(-5) M [using their salts: ZnCl2, CdCl2, LiCl, CuSO4, NiSO4, Al2(SO4)3, (NH4)2MoO4 on the lactoferrin (Lf) binding to the erythrocyte membrane receptors was studied. In the absence of metal ions, Scatchard's analysis showed the existence of two kinds of binding site: one with high affinity and low capacity, and the another with low affinity and high capacity. All these metals, excluding Zn2+ and Cd2+, at a concentration 10(-5) M decreased the affinity of Lf binding (Ka1) to the high-affinity receptors. In the presence of Zn2+ and Cd2+, only the low-affinity binding site was found. Significant inhibition on the affinity (Ka2) of the low-affinity class of receptors showed Zn2+, Al3+, and Mo6+. Depending on their concentration (10(-8)-10(-5) M), these ions enhanced to a different extent, the binding capacity of the both types receptors, but the effect did not correspond to the applied doses. Several explanations of the mechanism for influence of the metal ions on the Lf-receptor interaction is discussed.

Biological Transport↗
PubMed1998

Effect of lactoferrin on the phagocytic activity of polymorphonuclear leucocytes isolated from blood of patients with autoimmune diseases and Staphylococcus aureus allergy.

Phagocytic number (PN) and phagocytic index (PI) of neutrophils isolated from blood of patients with autoimmune diseases, allergy to Staphylococcus aureus and from blood of healthy individuals were examined. Our results concerning the influence of lactoferrin (Lf); (6.7 mg/l) on the PI of PMN showed that: 1) Lf enhances reliable PI of PMN at the 30-th minute starting the phagocytic reaction in patients with autoimmune disease in an active stage, in blood donors treated as healthy with the presence of autoantibodies, in patients with autoimmune diseases and proved autoantibodies against tissue, cell antigens and collagen, 2) Lf influences non-significantly PI of PMN in patients with autoimmune collagen diseases in remission, 3) Lf increases PI of PMN with 19% only in 58% from the assessed patients with Staphylococcus aureus, and 4) Lf decreases non-significantly PI of PMN in the healthy controls. Our studies on the effect of Lf on the phagocytic activity of PMN suggest that Lf has stronger effect on the PN compared to the PI: 1) Lf enhances with 86% the PN in patients with Staphylococcus aureus, 2) Lf increases PN of PMN in all of the assessed patients with autoimmune collagen diseases in active stage (mean with 72%), and 3) Lf increases PN of PMN in 4 from the 5 investigated healthy controls (mean with 22%). Our results show a "corrective" effect of Lf on the phagocytic functions in the investigated groups of patients. The possible mechanisms, by which Lf increases PN and PI of neutrophils, is discussed: 1) they may concern the antioxidative properties of Lf to block the iron ions in their catalytic inactive form or to take part as ferric-Lf in an oxidative-reduction processes on the plasma membrane and controlling transmembrane transport systems, 2) Lf decreases the negative surface charge and thus enhances the adherent ability of the PMN. Probably to this stimulated adherent ability dues the increased ingestion of bacteria in the presence of Lf, and 3) The "changed" membrane of PMN may have higher number receptors for Lf to bind more molecules of exogenous Lf. The increase of Lf binding which enhances the adherence and aggregation of neutrophils, facilitates the phagocytosis.

Adolescent↗
PubMed1998

The competition between transferrins labeled with 59Fe, 65Zn, and 54Mn for the binding sites on lactating mouse mammary gland cells.

Using a homologous competition of 54Mn-transferrin with Mn-transferrin and 65Zn-transferrin with Zn-transferrin, it was found that on the plasma membrane of lactating mouse mammary gland cells there are receptor binding Mn-transferrin and Zn-transferrin. The heterologous competition between labeled and nonlabeled Fe-transferrin, Mn-transferrin and Zn-transferrin, as well as almost equal affinity constants of cellular receptors toward the three metals by competition of Fe-transferrin suggests that one and the same receptor accepts all three metals from the transferrin molecule. The cell receptors therefore possess a polymetal binding function. A model and a mechanism for regulation of the transport metal flow toward the mammary gland cell acting like "automated switching over" are proposed.

Animals↗
PubMed1994

[Radioimmunological determination of glucagon in Bulgarian insulin substances].

The contents of glucagon in insulin substances ("Pharmachim" Ltd.) is determined in accordance to the needs of pharmaceutical production. The middle quantitative values and standart deviation are specified. Nevertheless that monocomponent and bovine conventional insulin substances pertain to groups of different purity they exibit the highest purity. Bovine conventional insulins exibit the greatest variability, while monocomponent insulins are destinctively homogenous. Single-peak insulin substances exhibit less purity, but this group is more homogenous. The middle quantitative value is within the admissible limitations. Porcine conventional insulins have high contents of glucagon as well as high values of standard deviation.

Animals↗
PubMed1994

[The determination of the somatostatin content in insulin substances].

30 different lots (batches) of insulin substances ("Pharmachim" Ltd.) are analysed and the contents of somatostatin is established. The middle quantitative values and the standard deviations are specific. Though that monocomponent and bovine conventional insulin substances pertain to groups of different purity they exhibit highest purity but also greatest variability, while single-peak and porcine conventional insulins show less purity but these groups are more homogenous.

Animals↗
PubMed1993

Lactoferrin binding to human platelets.

1. Platelets bind specifically lactoferrin. 2. The lactoferrin binding to the platelets depends on the concentration of labelled lactoferrin, the number of platelets, the time of incubation and pH. 3. The binding was characterized by two types of binding site: one with high affinity and low capacity, and another with low affinity and high capacity (respectively Kaff1 = 13.6 x 10(9) l/mol and about 40 binding sites, and Kaff2 = 1.23 x 10(9) l/mol and about 135 binding sites per platelet). 4. Both human transferrin and bovine lactoferrin compete with human lactoferrin for the receptors. 5. The presence of lactoferrin receptors on the platelet membrane surface is connected most probably with the effect(s) on the cell function(s) of these cells.

Binding Sites↗
PubMed1993

[The preparation of materials and the isolation of human genomic DNA for analysis].

The work reviews the usual and most convenient human samples (blood cells, fibroblasts, etc.) for extraction of DNA, storage conditions, DNA extraction approaches, and the criteria for assessment of quality and suitability of the extracted DNA for subsequent analysis. The aim of this work is to make professionals from different laboratory disciplines aware of the basic approaches to DNA sampling and storage in order to promote their further involvement in diagnostics and research based on DNA technology.

DNA↗
PubMed1993

[The determination of the biological activity of insulin by a radioreceptor method].

A new in vitro radioreceptor assay method for determining the biological activity of insulin substances is put forward. This method is designed mainly to serve the purposes of practice. It perfectly substitutes the biological, expensive labour-taking and slow pharmacopoeial method. It is reproducible, does not depend on the season and reduces the species differences to minimum by using a mixture of bovine and porcine insulins (Forth International Standard) as the source of unlabeled insulin. The rat liver membrane receptors (preparations) retained their insulin-binding ability up to 10 months, when stored at -18 degrees C-(-)20 degrees C. By means of this method the biological activity in different insulin preparations is established. It is found that this activity is highest in the monocomponent insulin substances, followed by the single-peak insulins and it's lowest in the conventional insulins.

Animals↗
PubMed1993

[Vasopressin as a neurotransmitter and neuromodulator].

Recent data about the antidiuretic hormone arginine vasopressin (AVP) are reviewed which show that except its well known peripheral endocrine functions, it has another not less important function as a neurotransmitter and neuromodulator in the central nervous system. AVP facilitates learning and memory consolidation. Data are also presented about the primary structure of AVP precursor and the sites of its synthesis, as well as about the AVP receptors and the mechanism of its action in different brain areas. Data are given about the ways of inactivation of its second messengers inositol-1,4,5-triphosphate and diacylglycerol. There are also data about AVP antipyretic effect in septum. A hypothesis is presented that the action of some nonsteroid antipyretic substances is mediated through V1-receptors of AVP in septum.

Animals↗
PubMed1993

[Problem solving of the clinical case-method type for the development of clinical thinking. The illustrative problem of galactosemia].

Problem-solving case approach is an effective method for teaching clinical concepts. This method makes medical students be aware of the significance of Biochemistry for the clinical practice. The students are stimulated to study basic biochemical principles. The complete text of a problem case on galactosemia is presented. This case, usually given to the students during the final seminar on carbohydrate metabolism reflects a real situation, in which the student feels responsible to make decisions. He has to make the diagnosis and prescribe a treatment. The student's actions are assessed and commented. The students took a great interest in that problem case and that shows that it is possible and necessary even in the second preclinical year to joint the theoretical principles with the future clinical practice.

Bulgaria↗
PubMed1988

Insulin action in vivo on a growth-related protein kinase in lactating mouse mammary gland.

1. A cytosol serine-protein kinase was isolated and partially purified from lactating mouse mammary gland which is cAMP-independent, inhibited by the bioflavonoid quercetin and probably connected to the growth of mammary cells. 2. After supra-physiological doses of insulin (0.4 IU daily) given in vivo the activity of this kinase rises 2.4 times, but at 5 times higher doses of insulin the activity was completely inhibited. 3. The biphasic effect of insulin suggests that this protein kinase might be connected to the growth effect of the hormone.

Animals↗