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E Cabib

Publications and source records attributed to E Cabib.

86 records · Page 5Linked to original sources
PubMed1971

The control of morphogenesis: an enzymatic mechanism for the initiation of septum formation in yeast.

Previous work with yeast has indicated that chitin is the specific component of the septum between mother and daughter cell. Experiments with synchronized cells show that chitin synthesis is initiated at a precise time in the cell cycle. Newly discovered features of the chitin synthetase system suggest how this specificity in location and timing can be achieved. The particulate chitin synthetase is shown to exist almost entirely in an inactive or zymogen state. The zymogen can be converted into an active form either by an enzyme (activating factor) present in yeast or by trypsin. The activating factor is found in a particulate fraction, but can be solubilized by mild sonic oscillation. A heat-stable protein, previously isolated from yeast and believed to inhibit chitin synthetase, has now been found to act as an inhibitor of the activating factor to which it binds very tightly. It is proposed that chitin synthetase, in the zymogen form, is uniformly distributed on the cytoplasmic membrane. At the time of septum initiation, vesicles carrying the activating factor would be directed to specific sites and bring about the localized conversion of the zymogen into the active form. A molecular model is thus introduced for processes of morphological change and differentiation.

Autoradiography↗
PubMed1970

Two forms of yeast glycogen synthetase and their role in glycogen accumulation.

The glycogen content of yeast rises dramatically just before the onset of the stationary phase of growth. Concomitantly, a rapid increase was found in the glucose 6-phosphate-independent (I) activity of glycogen synthetase, as well as in the total amount of enzyme. A mutant (GS 1-36) was obtained, which did not accumulate glycogen during growth. The synthetase from this strain was in the glucose 6-phosphate-dependent (D) form at all times. The total enzymatic activity of the mutant also increased sharply at the end of the logarithmic phase, although its maximal value was only one third that of the parent strain. Incubation with glucose of wild type resting cells from the logarithmic phase resulted in a slow accumulation of glycogen, which was accelerated after 20 min. At the same time a transformation from the D to I form of the enzyme was detected. The same slow initial rate of glycogen deposition was found with stationary cells of mutant GS 1-36, but the rate gradually declined to zero, rather than accelerating. The interconversion of the I and D forms was obtained with extracts from cells harvested during different phases of growth. Examination of the properties of the I and D forms showed that the latter was much more strongly inhibited by ATP at low glucose 6-phosphate concentration. These findings clearly establish the fundamental role of the I form in glycogen accumulation. When taken together with previous results, they also show that the physiological significance of the I-D interconversion depends on the concentration of glucose 6-phosphate. Under certain conditions glucsoe 6-phosphate appears to regulate directly the activity of the predominant form of the enzyme.

Adenosine Triphosphate↗