Showing papers in "Sub-cellular biochemistry in 1979"

Dehydrogenases of the plasma membrane.

Abstract: Oxidation-reduction reactions are widespread in biological systems and are basic to life processes and cellular metabolism. Nicotinamide-nucleotide-linked electron transport is generally part of a complex chain or array of carriers linked both structurally and functionally to cellular membranes. Some of the carriers may be loosely bound to the membrane or even “soluble” in the cytoplasm; others are structured as integral proteins of the membrane. The most widely studied are those of the electron-transport system found in and restricted to the inner mitochondrial membrane. Here, a sequence of components is organized mostly on the inner mitochondrial membrane with three sites of potential energy coupling to ATP formation (DePierre and Ernster, 1977).

The role of lipids in the structure and function of membranes.

Abstract: The increased knowledge of the properties of membrane lipids (Ansell et al, 1973) and of lipid-protein interactions (Singer, 1971; Lenaz, 1973, 1977; Vanderkooi, G, 1974) allows a better understanding of the role of lipids in membrane structure and functions Nevertheless, a unifying picture of such a role is lacking, and it is often tacitly assumed that lipids have different roles; this is indeed the main conclusion emerging from analysis of the literature In fact, lipids in membranes have different functions, affecting enzymic activity positively or negatively, being determinants of permeability properties and transport and being involved in the action of membrane binding sites and receptors Moreover, they are determinants of membrane phenomena involving fusion processes (eg, cell movement, pinocytosis, cell division, cell adhesion, secretion) In such functions, lipids may be specific or not The physical state of a lipid, besides the specific chemical nature of certain groups, appears to be very important in its functions It seems therefore appropriate to assign to lipids many different roles

The petite mutation in yeast.

Abstract: Bakers’ yeast, Saccharomyces cerevisiae, is one of the simplest of eukaryotic organisms. Its ability to grow on liquid or solid defined media with a short generation time renders it amenable to the powerful techniques that have been employed to elucidate the biochemistry and genetics of prokaryotes. It has consequently been used as a model eukaryote for many biochemical and genetic investigations. It has found particular favor in studies on the mechanism of mitochondrial assembly and the role of mitochondrial DNA (mtDNA), the reason being that this species of yeast is capable of surviving and growing in the absence of functional mitochondria, obtaining its ATP requirements through fermentative metabolism. Many different types of mutation affecting mitochondrial function have been studied, but one particular class of mutants stands out in terms of the contribution it has made. This class comprises the different kinds of extrachromosomal petite mutants. Such mutants have sustained gross deletions or total loss of mtDNA and are, in consequence, incapable of assembling mitochondrial ribosomes and carrying out mitochondrial protein synthesis. Petite mutants have been of particular value in investigating the role of mtDNA, establishing which mitochondrial proteins are synthesized extramitochondrially and constructing gene maps of mtDNA.

Structures, properties, and possible biologic functions of polyadenylic acid.

Abstract: Our original interest in preparing this review lay in the fact that no one had presented a thorough examination of the topic, with particular attention to the several possible biological functions of polyadenylic acid [poly(A)]. However, as we scrutinized the literature, one point cropped up repeatedly: those engaged in research efforts aimed at clarifying the physiological significance of poly(A) did not make full use of the current body of knowledge concerning the chemical properties of the homopolymer. Similarly, results of experiments that clarify aspects of the physical nature of poly(A) were never interpreted in terms of intracellular functions. Thus, two vast bodies of literature exist in roughly equal proportions, one concerning the biochemistry of poly(A), the other dealing with more physically oriented considerations, and the amount that either group draws on the knowledge or experience gained by the other is small. It was therefore obvious to us that a deficit was present in the field of polyadenylic acid research: no source of knowledge concerning all facets of the biology and chemistry of poly(A) existed. Consequences of the lack of discussion between chemists and molecular biologists engaged in work involving poly(A) were manifest. Experimental results based on quantitation of poly(A) · polyuridylic acid (poly(U)] hybrids prepared under conditions wherein the triplex [poly(A) · 2 poly(U)] may exist is one example. Another is the attitude with which the structure of poly(A) is approached by most biologists. Few papers dealing with the molecular biology of poly(A) give consideration to the different structural forms that the polymer may assume. Despite overwhelming evidence from chemical and physical studies that this polymer is unique in many respects and that an alteration in experimental conditions may induce a radical change in polymeric structure, little consideration is given to this information. As a final example, the researchers attempting to define the nature of the poly(A)-binding proteins appear to be unaware of classes of enzymes that interact with poly(A) and are not cognizant of the consequences of the partially stacked structure of the polymer relevant to amino acid and protein binding. Thus, the knowledge regarding the many aspects of poly(A) chemistry and biochemistry are, in our opinion, in need of organization and presentation in one place. We feel that such an effort will be of importance to both the biochemist and the chemist, since no review of the chemical and physical properties of poly(A) has been published in more than a decade, and the last ten years have seen the most significant advances in knowledge concerning the structure of poly(A) and its interactions with cations, low-molecular-weight organic compounds, and macromolecules. Accordingly, we have divided our manuscript approximately in two; the first part deals with the biochemical and subcellular aspects of poly(A), and because of the biochemical importance of the structure of poly(A), the second half concentrates on this topic—but includes, as well, sections on metals, complementary monomers, and polymers that interact with poly(A).

Transport Processes in Membranes: A Consideration of Membrane Potential across Thick and Thin Membranes

Abstract: Any phase that acts as a barrier preventing mass movement but allowing restricted or regulated passage of one or several species through it may be defined as a membrane. This could be a solid or liquid or even a gas (see Buck, 1976) containing ionized or ionizable groups, or it may be completely unionized. All membranes are active in an operational sense when used as barriers to separate two solutions or phases unless they are too fragile or too porous. Membranes may be broadly classified into natural and artificial or man-made. Natural membranes are thin (<100 A), whereas artificial polymeric membranes that have proved their usefulness in several successful unit processes are thick (more than a few micrometers), even though thin (≥ 50 A) membranes of parlodion have been prepared (Lakshminarayanaiah and Shanes, 1963) and characterized (Lakshminarayanaiah, 1965a; Lakshminarayanaiah and Shanes, 1965). In addition, lipid bilayer membranes that are also thin (∼50 A), since the time they were first generated in 1962 by Mueller et al. (1962a, b; 1963), have assumed great interest and importance. This is probably due to their close resemblance to natural membranes of living systems. Other model membrane systems of interest and significance are the so-called “liposomes,” which are also called “Bangosomes” (DeGier et al., 1968) after their discoverer, Bangham (Bangham et al., 1965). Several properties of phospholipid liposomes or vesicles or both were reviewed by Bangham (1968). A rough classification of several types of membranes according to their physical dimensions and chemical structure is shown in Figure 1.

Computer simulation of density-gradient centrifugation.

Abstract: Modern biochemical techniques are continuously refined to produce new and improved results. Improvements in the useful power of a biochemical technique can in principle be achieved in two ways. One is the classic trial-and-error approach whereby the parameters of the experimental conditions are varied one by one until a suitable set of conditions is found. The other way of improving or optimizing a technique is theoretical. The desired quality of the outcome of the experiment in question (i.e., the degree of analytical reliability or the desired power of resolution) is considered in physicochemical terms, and the experimental conditions that are needed to achieve this quality are calculated.

Crown-Gall and Agrobacterium tumefaciens: Survey of a Plant-Cell-Transformation System of Interest to Medicine and Agriculture

Abstract: Crown-gall tumors (Figure 1) on various plants were described in Europe by several naturalists as early as the last century, and were generally ascribed to the action of insects or mechanical injury (Smith et al., 1911). According to Smith et al. (1911), Cavara (1897) in Italy was the first to demonstrate the bacterial nature of the disease around 1897 by means of inoculations from pure cultures. However, his studies, as well as those of other writers of southern Europe on this subject, were generally overlooked. In 1907, Smith and Townsend (1907) submitted a paper to Science in which they reported their findings on the causal agent of crown-gall tumors. Their results also showed that a bacterium was the etiological agent of the neoplasm, and they called it Bacterium tumefaciens. Their finding attracted immediate interest, especially from animal pathologists (Jensen, 1910, Levin, J., and Levine, 1918), since in their eyes it was the first instance in which a neoplasm could be associated with an infectious agent and therefore induced under defined experimental conditions. While some animal pathologists started to search for bacteria in animal neoplasms, it was shown that the causal agents of some animal tumors were filtrable (“viral”) and thus not of bacterial origin (Rous, 1911; Rous and Murphy, 1914). As a result, crown-gall disease and its infectious agent, more recently called Agrobacterium tumefaciens (Conn, 1942), became more and more the subject of studies of plant pathologists. However, with the years, fundamental similarities in the cellular processes of different cells were recognized. Much fundamental biological and especially genetic knowledge accumulated from the study of bacteria and their viruses. Cancer researchers made the finding, among other findings, that different agents such as viruses, chemicals, and irradiation could induce neoplasms, and some started to recognize that the question whether there is a common subcellular and molecular basis of neoplasms might be the fundamental problem to be answered. On the other hand, agricultural scientists, in their search for creating new genetic variability among plants, became interested in the possibility of modifying plant cells at the molecular level. With these prospects, the crown-gall disease, and its infectious agent, Agrobacterium tumefaciens, attracted more and more interest among biologists from different fields in succeeding years.