Subcellular localization of γ-glutamyltransferase in calf thymocytes

Abstract
The subcellular localization of .gamma.-glutamyltransferase [EC 2.3.2.2] in calf thymocytes was investigated and compared with that of alkaline phosphodiesterase I, alkaline nitrophenyl phosphatase, succinate-tetazolium oxidoreductase (succinate-INT reductase) and lactate dehydrogenase, after 2 different methods of cell disruption and differential centrifugation. Most of the activity was recovered in the crude membrane fractions (43.0%) but significant amounts co-pelleted with the large-granule (mitochondria) fractions (31%). The specific activity of the .gamma.-glutamyltransferase in the purified plasma membrane was 30-50 times that of the enzyme in the cell homogenate and had a similar subcellular distribution to the plasma-membrane markers, alkaline phosphodiesterase I and alkaline nitrophenyl phosphatase. .gamma.-Glutamyltransferase is apparently a plasma-membrane-bound enzyme, and its location in other subcellular fractions is probably due to contamination with plasma-membrane vesicles.

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