Presence of a transglutaminase activity in rat liver lysosomes

The intracellular distribution of rat liver transglutaminase has been investigated by centrifugation methods. When measured in presence of Ca++ the enzyme is mainly present in the unsedimentable fraction of the homogenate. When assayed in absence of Ca++, the enzymatic activity exhibits a distribution pattern like that of lysosomal markers, both after differential and isopycnic centrifugation. The enzyme shows the phenomenom of structure linked latency and can be unmasked parallel with acid phosphatase by freezing and thawing. The origin of this transglutaminase is discussed; it is proposed that it is a genuine constituent of lysosomes.