G. Luers et al., BIOGENESIS OF PEROXISOMES - ISOLATION AND CHARACTERIZATION OF 2 DISTINCT PEROXISOMAL POPULATIONS FROM NORMAL AND REGENERATING RAT-LIVER, The Journal of cell biology, 121(6), 1993, pp. 1271-1280
According to Poole et al. (1970. J. Cell Biol. 45:408-415), newly synt
hesized peroxisomal proteins are incorporated uniformly into peroxisom
es (PO) of different size classes, suggesting that rat hepatic PO form
a homogeneous population. There is however increasing cytochemical an
d biochemical evidence that PO in rat liver are heterogenous, undergoi
ng significant modulations in shape and size in process of PO morphoge
nesis (Yamamoto and Fahimi, 1987. J. Cell Biol. 105:713-722). In the p
resent study, the kinetics of incorporation of newly synthesized prote
ins into distinct PO-subpopulations have been studied using short-term
in vivo labeling (5-90 min). Two distinct ''heavy'' and ''light'' cru
de PO fractions were prepared by differential pelleting from normal an
d regenerating liver, and highly purified PO were subsequently isolate
d by density-dependent metrizamide gradient centrifugation according t
o Volkl and Fahimi (1985. Eur. J. Biochem. 149:257-265). The peroxisom
al fractions banded at 1.20 and 1.24 g x cm-3. They differed in their
mean diameters and form-factors and particularly in respect to the act
ivity of beta-oxidation enzymes which was higher in the ''light'' PO.
Whereas the ''light'' PO exhibited a single immunoreactive band with t
he antibody to the 70-kD peroxisomal membrane protein the ''heavy'' PO
contained an additional (68 kD) band. In pulse-labeling experiments '
'light'' PO showed clearly a higher initial rate of incorporation than
the ''heavy'' PO. The relative specific activity in the ''heavy'' PO
fraction, however increased progressively reaching that of ''light'' P
O by 90 min. These observations provide evidence for the existence of
different PO populations in rat liver which differ in their morphologi
cal and biochemical properties as well as in their rates of incorporat
ion of new proteins.