### A. Overview

Extracellular purines (adenosine, ADP, and ATP) and pyrimidines (UDP and UTP) are important signaling molecules that mediate diverse biological effects via cell-surface receptors termed purine receptors. In this review particular emphasis is placed on the discrepancy between the

/pdf/receptors-for-purines-and-pyrimidines-56f78tnpew.pdf

Receptors for Purines and Pyrimidines

/pdf/inositol-trisphosphate-and-diacylglycerol-as-second-4drzjsg27y.pdf

Inositol trisphosphate and diacylglycerol as second messengers.

During the course of purifying nerve growth factor from the submaxillary gland of the mouse, Cohen (1960) and Levi-Montalcini and Cohen (1960) noticed that daily injections of certain gland extract fractions into newborn mice produced developmental changes that could not be ascribed to nerve growth factor. These changes included precocious opening of the eyelids (7 days compared to the usual 14 days) and a similar early eruption of the incisors. Using these gross anatomical changes as an assay, Cohen (1962) proceeded to isolate the active factor — a polypeptide which he termed epidermal growth factor (EGF).

Epidermal growth factor

The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded byan outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.

/pdf/the-bacterial-cell-envelope-o3k9u4ycci.pdf

The Bacterial Cell Envelope

The bisindolylmaleimide GF 109203X is a potent and selective inhibitor of protein kinase C.

The release of enzymes by osmotic shock from Escherichia coli in exponential phase.

Purification and properties of 5-nucleotidase

A group of hydrolytic enzymes, including phosphatases and nucleases, is selectively released from E. coli and certain other Gram-negative bacteria by a process designated as osmotic shock. This procedure involves exposure of the cells to ethylenediaminetetraacetate (EDTA) in 0.5 molar sucrose followed by a sudden osmotic transition to cold, dilute MgCl(2). Osmotic shock also results in an alteration of the permeability barrier of the bacterial cell and a depletion of the pool of acid-soluble nucleotides, but there is no loss of viability. On being restored to growth medium, the shocked cells recover after a lag period. Formation of spheroplasts by treatment with EDTA and lysozyme leads to selective release of the same group of enzymes. We believe that the selectively released enzymes are confined in a region between the bacterial cell wall and the cytoplasmic membrane. Histochemical studies indicate such a localization. Further, the enzyme activities are measurable with intact cells, even when the substrate is a nucleotide, to which whole cells are impermeable. Another piece of evidence concerns a mutant E. coli with a defective cell wall. In contrast to normal bacteria, this organism loses one of these enzymes into the medium in the course of growth. After osmotic shock, the bacteria show reduced uptake of sulfate,betagalactosides, galactose, and certain amino acids. Furthermore, the shock treatment causes the release of nondialyzable factors able to bind sulfate, galactose, and the same amino acids. A possible interpretation of these observations is the following: the binding proteins occupy sites near the bacterial surface, and they may be components of active transport systems responsible for the concentrative uptake of these nutrients.

Selective Release of Enzymes from Bacteria

Serum causes a 4-fold increase in 86Rb+ (a K+ tracer) influx in quiescent 3T3 mouse fibroblast cells. It is one of the earliest changes caused by serum, being seen in 2 min and reaching a maximum in 10 min. Removal of serum causes rapid reversal of this effect. Serum acts mainly by increasing the maximum velocity, Vmax, of entry. Ouabain inhibits entry of 86Rb+ (82-90%) both in the presence and absence of serum, but does not alter exit. The rapid increase in cation influx is unaffected by cycloheximide and by changes in cyclic AMP and GMP. Low concentrations of insulin, epidermal growth factor, and prostaglandins (E1 and F2alpha) produced a smaller (80%) activation of 86Rb+ entry. Ouabain, at a level that inhibits cation influx, also prevents the onset of DNA synthesis following serum addition; this is reversible effect dependent on the concentration of K+ in the medium. This suggests that cation pumping activity may be required for initiation of DNA synthesis.

Leon A. Heppel

Papers

The release of enzymes by osmotic shock from Escherichia coli in exponential phase.

Purification and properties of 5-nucleotidase

Selective Release of Enzymes from Bacteria

Serum rapidly stimulates ouabain-sensitive 86-RB+ influx in quiescent 3T3 cells.

The Release of Ribonuclease into the Medium When Escherichia coli Cells Are Converted to Spheroplasts