Microheterogeneity and intrahepatic localization of human and rat liver cytosolic alanine aminotransferase.
Native human cytosolic alanine aminotransferase (EC 2.6.1.2) was found to be a homodimer consisting of two 55 kDa subunits. The human enzyme was more cationic and more susceptible to heat inactivation and heavy metal-inhibition than its rat homologue. Isoelectric focussing separated three human isoforms and four rat isoforms of cALT that differed in their isoelectric points. Two subtypes of the enzyme which differed in apparent molecular weight on sodium dodecylsulfate polyacrylamide gel electrophoresis were detected in rat, the liver type and the muscular type. This microheterogeneity was not found for human cytosolic alanine aminotransferase. Immunohistochemical studies revealed that the rat liver enzyme was exclusively localized in periportal hepatocytes, consistent with its role in gluconeogenesis. In human hepatocytes the plasma membrane was intensely stained, implicating an intracellular localization near the plasma membrane.
Matsuzawa
T
T
Department of Biochemistry, School of Medicine, Fujita Health University, Toyoake, Aichi, Japan. tmatsuza@fujita-hu.ac.jp
Kobayashi
T
T
Ogawa
H
H
Kasahara
M
M
D000410:Alanine Transaminase / Q000737:chemistry* / Q000302:isolation & purification*; D000818:Animals; D002412:Cations; D002462:Cell Membrane / Q000201:enzymology; D002845:Chromatography; D003600:Cytosol / Q000201:enzymology*; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007150:Immunohistochemistry; D007525:Isoelectric Focusing; D008099:Liver / Q000648:ultrastructure*; D008297:Male; D008670:Metals / Q000494:pharmacology; D008875:Middle Aged; D008970:Molecular Weight; D051381:Rats
D002412:Cations; D004791:Enzyme Inhibitors; D008670:Metals; D000410:Alanine Transaminase