Enzyme yeast cell

In 1878 the term enzyme, Greek for "in yeast," was proposed (8). It was reasoned that chemical compounds capable of catalysis, ie, ptyalin (amylase from sahva), pepsin, and others, should not be called ferments, as this term was already in use for yeast cells and other organisms. However, proof was not given for the actual existence of enzymes. EinaHy, in 1897, it was demonstrated that ceU-free yeast extract ("zymase") could convert glucose into ethanol and carbon dioxide in exactiy the same way as viable yeast cells. It took some time before these experiments and deductions were completely understood and accepted by the scientific community. 

Because enzymes can be intraceUularly associated with cell membranes, whole microbial cells, viable or nonviable, can be used to exploit the activity of one or more types of enzyme and cofactor regeneration, eg, alcohol production from sugar with yeast cells. Viable cells may be further stabilized by entrapment in aqueous gel beads or attached to the surface of spherical particles. Otherwise cells are usually homogenized and cross-linked with glutaraldehyde [111-30-8] to form an insoluble yet penetrable matrix. This is the method upon which the principal industrial appHcations of immobilized enzymes is based. 

A solution to the problem of introns is to isolate mRNA extracted from the human pancreas cells that make insulin. These cells are rich in insulin mRNA from which introns have already been spliced out. Using the enzyme reverse transcriptase it is possible to convert this spliced mRNA into a DNA copy. This copy DNA (cDNA), which carries the uninterrupted genetic information for insulin can be cloned. Although yeast cells (Saccharomyces) can splice out introns it is normal practice to eliminate them anyway by cDNA cloning. 

In Saccharomyces cerevisiae, as in most eukaryotic cells, the plasma membrane is not freely permeable to nitrogenous compounds such as amino acids. Therefore, the first step in their utilization is their catalyzed transport across the plasma membrane. Most of the transported amino acids are accumulated inside the yeast cells against a concentration gradient. When amino acids are to be used as a general source of nitrogen, this concentration is crucial because most enzymes which catalyze the first step of catabolic pathways have a low affinity for their substrates. 

Norton S, D Amore T (1994) Physiological effects of yeast cell immobilization applications for brewing. Enzyme Microb Technol 16 365-375... 

Fig. 6.—How the presence of different enzymes in a yeast cell was established.

When in later years Krebs reviewed the major points which had to be established if the cycle was to be shown to be operative in cells, the obvious needs were to find the presence of the required enzymes and to detect their substrates. As the substrates are present in the cycle in catalytic amounts their accumulation required the use of inhibitors. Krebs also stressed that rates of oxidation of the individual substrates must be at least as fast as the established rates of oxygen uptake in vivo, an argument first used by Slator (1907) with reference to fermentation A postulated intermediate must be fermented at least as rapidly as glucose is. (See Holmes, 1991). This requirement did not always appear to be met. In the early 1950s there were reports that acetate was oxidized by fresh yeast appreciably more slowly than the overall rate of yeast respiration. It was soon observed that if acetone-dried or freeze-dried yeasts were used in place of fresh yeast, rates of acetate oxidation were increased more than enough to meet the criterion. Acetate could not penetrate fresh yeast cell walls sufficiently rapidly to maintain maximum rates of respiration. If the cell walls were disrupted by drying this limitation was overcome, i.e. if rates of reaction are to be... 

McGrath, J. P., Varshavsky, A., and Byers, B. The yeast cell cycle gene CDG34 encodes a ubiquitin-conjugating enzyme. Science 1988,... 

The early history of enzymes is associated widi die process of brewing and die production of wine because of die economic importance of these processes in Europe in the nineteenth century. Following on from the work of Pasteur, it was Buchner and others who showed that an extract of yeast carried out fermentation (i.e. die conversion of glucose to alcohol) as well as die yeast cell itself. The agents diat did diis catalysis in the extract were simply described as in yeast which, from the Greek enQn) and zyme, is the name enzyme was derived. 

The lytic enzyme systems, active against yeast cell walls, usually contain l,3-/ -glucanases, proteases, mannanases, chitinases, and 1,6-) -glucanases. The proportion of those enzyme activities, their action pattern, synergism, and dependence on inhibitors constitute the activity profile... 

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