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YEAST CELL BIOMASS AS a POTENTIAL SOURCE of MAGNESIUM BIOPLEXES – a REVIEW Stanis³aw

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YEAST CELL BIOMASS AS a POTENTIAL SOURCE of MAGNESIUM BIOPLEXES – a REVIEW Stanis³aw POLISH JOURNAL OF FOOD AND NUTRITION SCIENCES Pol. J. Food Nutr. Sci. 2004, Vol. 13/54 No 3, pp. 223–232 YEAST CELL BIOMASS AS A POTENTIAL SOURCE OF MAGNESIUM BIOPLEXES – A REVIEW Stanis³aw B³a¿ejak, Wanda Duszkiewicz-Reinhard Department of Food Biotechnology and Microbiology, Agricultural University of Warsaw, Warsaw Key words: yeasts, magnesium, bioplexes, bioaccummulation The capability of yeasts for binding magnesium in the amounts exceeding its physiological demand affords an opportunity for exploiting those organisms as a natural source of a deficient bio-compound in a diet of contemporary humans. The mechanism of cation binding with yeast cells demonstrating first the character of chemisorption followed by intracellular bioaccummulation, may lead to the formation of organic linkages called “bioplexes”. Magnesium ions bound with proteins in the form of the so-called “bioplexes” are very well assimilated by human and animal organisms, thus they may be an alternative to pharmacological supplementation at increasingly observed magnesium deficiency. After appropriate treatment, reducing the content of nucleic acids, cellular biomass of yeasts may not only be a valuable source of protein and vitamins but also of magnesium, especially when used in the form of protein-mineral preparations. INTRODUCTION become a valuable source of natural bioplexes. It opens up perspectives for a wider application of yeasts in the produc- Proper balancing of dietary components is crucial to tion of ready protein-mineral preparations or food additives human’s health. A key role of metabolic processes regula- enriching diets with deficient elements. tors in living organisms is ascribed to macro- and microele- ments. Advance in food technology results in the produc- SIGNIFICANCE OF MAGNESIUM TO THE PHYSIOLO- tion of new foodstuffs on the one hand and is often found to GY OF HUMANS change the quantitative and qualitative composition of essential nutrients in the processed raw materials on the Essential dietary constituents include bioelements, e.g. other. In consequence, food additives are more commonly magnesium, zinc, chromium, cobalt, manganese, copper, applied to improve the nutritive value of food so as to meet selenium or iron, which actively participate in many meta- consumers’ demands. Still, measures taken are not always bolic pathways at a cellular level of all living organisms. Of sufficient to provide the optimal level of nutrients in a con- the bioelements enumerated, a unique role is ascribed to temporary diet. At present, deficiency of one of the macro- magnesium which – as an integral component of coenzymes elements only, namely magnesium, has been estimated to or prostetic groups – activates over 300 enzymes (mainly affect from 50% to 80% of the Polish population depending kinases) that determine the proper course of the main vital on age. Often pharmacological supplementation does not processes, including glycolysis, DNA replication, synthesis produce the desired effects, mainly due to low availability of of nucleic acids, biosynthesis of proteins, and transfer macro- and microelements from ready preparations. through cytoplasmatic membranes [Hartwig, 2001]. Many microorganisms, including strains of Saccharomy- This element serves as a specific regulator and activator ces and Candida yeast genera, commonly accepted and ack- of multiple physiological processes. In nerve-muscle junc- nowledged as safe, demonstrate the capability for natural tions it demonstrates antagonistic activity against calcium binding of elements present in the environment, often in the ions, thus inhibits release of a neurotransmitter – acetylcho- amounts considerably exceeding their physiological line – and consequently reduces excitability of nerves and demand. Metal ions adsorbed on the cell’s surface may next muscles [Watson & Vaughan, 2001]. be a subject of intracellular bioaccummulation. This way Magnesium regulates the production of cyclic adenosine yeasts produce metal-protein complexes called metalopro- monophosphate (cAMP) mediated by adenylate cyclase teins or more generally – bioplexes. Macroelements (e.g. enzyme. This way it affects numerous physiological pro- magnesium) adsorbed to proteins are available by human cesses, including degradation of reserve energetic substra- and animal organisms far better than their inorganic or tes, aggregation of thrombocytes, excretion and functioning organic salts [Vandergrift, 1991; Mardarowicz, 1997]. of parathyroid gland hormones [Stryer, 1997]. Cellular biomass of yeasts, rich in protein with balanced Magnesium participates also in lipid metabolism. By amino acid composition and good digestibility, may also affecting the activity of lipoprotein lipase it determines the Author’s address for correspondence: Stanis³aw B³a¿ejak, Department of Food Biotechnology and Microbiology, Agricultural University of War- saw, Warsaw, ul. Nowoursynowska 159c, 02-787 Warszawa, Poland; e-mail: [email protected] 224 S. B³a¿ejak & W. Duszkiewicz-Reinhard concentration of cholesterol in blood. Reduced magnesium mational change as a result of which the protein gains cata- level in blood favours an increase in the concentration of lytic activity. An example of this mechanism is the activation low-density cholesterol fraction (i.e. LDL fraction unfavour- of glutamate synthetase taking part in nitrogen metabolism able to health) and a concurrent decrease in the level of in eukaryotic cells [Walker, 1994]. high-density cholesterol (HDL fraction) [Pasternak, 1999]. In the human organism, magnesium is the fourth macro- Magnesium cation has been reported to affect directly element, after sodium, potassium and calcium, in respect of cardiac muscle and smooth muscular coat of blood vessels, their concentration [Watson & Vaughan, 2001]. Its content and to counteract arrhythmia. Its high blood concentration in the body of an adult man ranges from 250 to 350 mg per decreases the contractility of the cardiac muscle [Watson & kg of body mass. It occurs mainly in bones where its con- Vaughan, 2001; G³owania et al., 2000]. centration reaches ca. 51% of its total content in the body. Mg2+ ions actively participate in oxidative phosphoryla- It concentrates also in cell interiors (ca. 45%) as well as tion which results in the formation of high-energy compounds other organs and tissues (ca. 4%). Nearly 60% of magne- being a source of energy to anabolic processes [Stryer, 1997]. sium accumulated in bones is subject to constant exchange. Magnesium, as an indispensable agent activating a In blood plasma, 55% of that macroelement occur in an sodium-potassium pump (Na+/ K+ - ATPs), plays a key role ionized form, 32% are bound with proteins, and another in maintaining membraneous gradient concentration of 13% form complexes with ATP [Walasek, 1998]. sodium and potassium. The concentration gradient of the Demand of the human organism for magnesium is diver- enumerated ions generates electric potential at both sides sified depending on age, lifestyle or type of work perfor- of cytoplasmatic membrane which is then applied for the med. Recommended daily allowance for magnesium is transport of glucose, amino acids, phosphates, and other 280–300 mg for women and 350–400 mg for men [Paster- substances [Watson & Vaughan, 2001; Pasternak, 1999]. nak, 2000; Kunachowicz et al., 1998]. Magnesium serves also as an activator of a calcium A constant magnesium level in blood serum at reduced pump (Ca2+ - ATPs) which in turn regulates the concentra- or inhibited absorption is maintained through magnesium tion of Ca2+ ions in cells [Walker, 1994]. release from the skeletal system and soft tissues. When Apart from a number of activating and regulatory func- magnesium level of blood serum falls down below tions, this element is also an important stabiliser of the ter- 0.7 mmol/L, symptoms of hypomagnesaemia are likely to tiary structure of proteins and nucleic acids. In the case of occur, which is manifested by enhanced nervous and muscu- DNA, it participates in the formation of nucleosomes and lar excitability and in extreme cases may lead to the state of the consolidation of chromosome structure. It is also coma. Hypomagnesaemia impairs functioning of the circu- responsible for the stabilisation of ribosomes by participa- latory system, i.e. causes disorders in cardiac performance ting in binding of their sub-units, thus it is crucial in the (arrhythmia), and an increase in arterial blood pressure translation process [Wêgleñski, 1995]. which is sometimes accompanied by a disease referred to as Magnesium serves also other significant functions rela- stenocardia and spasm of coronary arteries [Walasek, 1998]. ted to protein synthesis, because tRNA is able to bind Other symptoms linked directly with insufficient supply of that amino acids only in the presence of that element [Hartwig, ion refer to changes psychical in character, including anxiety 2001; Walker, 1994]. state, depressions, and psychoses [Watson & Vaughan, 2001]. In addition, Mg2+ ions stabilize mitochondrial membra- In addition, magnesium deficiency has been observed to nes and the mitochondria themselves [Zaj¹c, 2000; Walker, accompany some neoplastic diseases [Rudziñski, 1998]. 1994], as well as the structures of polysaccharides and lipids [Rees & Stewart, 1997]. MAGNESIUM DEFICIENCY – CAUSES AND PROPHY- This macroelement has building functions as well. It par- LAXIS ticipates in the formation and building of bones, teeth, and soft tissues. It contributes to the formation of durable amor- In
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