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J L Mego

Publications and source records attributed to J L Mego.

At least 37 records · Page 2Linked to original sources
PubMed1972

An adenosine triphosphate-dependent stabilization of proteolytic activity in heterolysosomes. Evidence for a proton pump.

1. Homogenization of mouse kidneys or livers in 0.25m-sucrose buffered with tris-acetate, pH7.3, resulted in a decreased rate of proteolysis within isolated heterolysosomes containing injected (125)I-labelled albumin when these particles were incubated at 35 degrees C. Proteolysis in mouse kidney or liver heterolysosomes isolated from homogenates made in 0.25m-sucrose buffered at pH7.3 was stimulated by pH5 buffer or by additions of ATP. 2. A greater inhibition of proteolysis was produced by including bicarbonate or pH8 borate buffers in the incubation media, and this inhibition was also reversed by ATP. 3. Other nucleoside triphosphates were not as effective as ATP, but GTP and ITP were more effective than CTP or UTP. ADP, AMP, or adenosine 3':5'-cyclic monophosphate were completely without effect. 4. Although ATP prevented some heterolysosome breakage in media containing bicarbonate, the primary effect appeared to be to promote proteolytic activity. 5. These observations are consistent with the presence of a proton pump in the heterolysosome membrane, which functions to maintain intralysosomal pH in alkaline media.

Adenine Nucleotides↗
PubMed1971

The effect of pH on cathepsin activities in mouse liver heterolysosomes.

1. Mouse liver heterolysosomes containing (125)I-labelled albumin were incubated at 35 degrees C in 0.25m-sucrose-0.05m-mercaptoethanol, and various concentrations of buffers at pH4, 5, 7 or 8, and the degradation of intraparticulate protein was measured. 2. Buffers at pH4, 7 or 8 inhibited proteolytic activity and the inhibitions were greater with increasing concentrations of buffers. Tris-acetate buffer, pH8, was a more effective inhibitor. Tris-acetate buffer, pH5, neither inhibited nor stimulated proteolytic activity at concentrations up to 0.1m. 3. Inhibition by pH8 buffers could be accounted for by increased breakage rates of heterolysosomes. 4. Preincubation of heterolysosomes in 0.2m-sodium bicarbonate inhibited proteolytic activity when the particles were washed free of bicarbonate, but the inhibition was reversed if these particles were incubated in media containing pH5 buffer. The inhibition was shown not to be due to an increased breakage of heterolysosomes. 5. It was concluded that the pH within heterolysosomes is about 5, and it is possible to alter reversibly the pH within these particles. The possibility for the existence of an intralysosomal buffering system which maintains the pH at about 5 in heterolysosomes is discussed. This buffering system may be related to the presence of large quantities of acidic lipoproteins in lysosomes observed by other investigators.

Acetates↗
PubMed1967

The use of formaldehyde-treated 131-I-albumin in the study of digestive vacuoles and some properties of these particles from mouse liver.

The trichloroacetic acid-soluble radioactivity released during incubation of mouse liver particles containing intravenously injected formaldehyde-treated (131)I-albumin consisted almost entirely of (131)I-iodotyrosine. The material was shown to be excreted into the medium and was not due to disruption of the particles by acid. Triton X-100 or the absence of sucrose in the medium inhibited hydrolysis of the particle-associated labeled protein. This inhibition was due to disruption of the digestive vacuoles and dilution of the protein and cathepsins in the suspending medium. These results and other experimental evidence strongly suggest that the (131)I-albumin-containing liver particles are digestive vacuoles. The results also establish that (131)I-albumin may be used to study these vacuoles. High concentrations of sucrose (1 M) inhibited degradation of intraparticulate protein. However, 1 M salts inhibited only the rate of the digestion. Sucrose had an inhibitory effect on a crude cathepsin preparation, and salts stimulated the activity when (131)I-albumin was used as substrate. The effect of high sucrose concentrations as an inhibitor of protein hydrolysis within digestive vacuoles was, therefore, most likely due principally to an inhibition of cathepsin activity within the vacuoles. The effect of salt was probably caused by a stimulation of both intra- and extra-particulate cathepsin activities, although 0.5-1.0 M KCl appeared to protect the particles.

Albumins↗