The synthesis and turnover of rat liver peroxisomes. I. Fractionation of peroxisome proteins

Peroxisomes in inner adrenocortical cells of fetal and adult guinea pigs

Abundant membrane-bounded granules, 0.1-0.45 microm in diameter, occur among the elements of the smooth-surfaced endoplasmic reticulum in zona fasciculata and zona reticularis adrenocortical cells of guinea pigs. Acid phosphatase cannot be cytochemically demonstrated in them, and they are therefore distinct from lysosomes. Incubation in medium containing 3,3'-diaminobenzidine results in dense staining of the granules, identifying them as peroxisomes. These small peroxisomes increase in number as fetal adrenocortical cells differentiate, and they appear to arise from dilated regions of endoplasmic reticulum. They maintain interconnections with the smooth endoplasmic reticulum and with one another.

Further evidence to suggest that microbodies do not exist as individual entities

Male wild-type mice (Cs(a) strain) were treated with ethyl-alpha-p-chlorophenoxyisobutyrate (CPIB), a hypolipidemic drug which enhances hepatic catalase synthesis and induces rapid and significant increase in the number of microbody (peroxisome) profiles in liver cells. Numerous microbody profiles, several of them appearing in clusters and retaining membranous continuities, were observed in liver cells of CPIB-treated mice. They showed a significant variation in size and configuration, and the presence or absence of the nucleoid or core did not appear to bear any relation to the size or shape of microbody profiles. Nucleoids were encountered frequently in microbody profiles measuring as small as 0.1 mu in diameter. Numerous continuities between two or more anucleoid and/or nucleoid-containing microbody profiles of different sizes and shapes were seen. These findings are inconsistent with the concept that the smaller peroxisomes are the possible precursors or progenitors of their larger counterparts. Detailed examination of numerous electron micrographs revealed irregular dilatations and tortuosities of the endoplasmic reticulum (ER) containing electron-opaque peroxisomal material displaying the characteristic appearance of matrix and usually containing irregular cores. Transitions of rough ER to smooth ER in which microbody proteins accumulated were also apparent. Numerous continuities between several microbody profiles and continuities between microbody profiles and ER are interpreted as accumulations of peroxisomal proteins in dilated tortuous channels of ER. These observations strongly suggest that the microbody proteins constitute a common pool, circulating constantly in the dilated ER channels. The size, shape and number of microbody profiles appear to reflect the amount of peroxisomal proteins present in the pool. These observations clearly suggest that the microbodies do not exist as individual entities.

Cytochemical localization of catalase in glyoxysomes isolated from maize scutella

The localization of catalase in isolated maize scutellum glyoxysomes was investigated by means of the diaminobenzidine histochemical reaction. Only the membranes of the glyoxysomes become heavily stained after incubation with diaminobenzidine and H(2)O(2). If the glyoxysomes are lysed with Tricine buffer at pH 9, 70% of the catalase is solubilized, while the remaining 30% is tightly bound to an insoluble fraction formed mostly by glyoxysomal membranes. This suggests that catalase may be present also in the matrix of the glyoxysomes. The lack of staining of the matrix with diaminobenzidine is probably due to the high concentration of catalase in the membranes of the organelles.

Peroxidase activity in rat liver microbodies after amino-triazole inhibition

The in vivo effects of 3-amino-1,2,4-triazole (AT) on the fine structure of microbodies in hepatic cells of male rats has been studied by the peroxidase-staining technique. Within 1 hr of intraperitoneal injection AT abolishes microbody peroxidase-staining, and the return of staining coincides temporally with the known pattern of return of catalase activity following AT inhibition; this is further evidence that the peroxidase staining of microbodies is due to catalase activity. Peroxidase staining reappears in the microbody matrix without evidence of either massive degradation or rapid proliferation of the organelles. Furthermore, during the period of return of activity, ribosomal staining occurs adjacent to microbodies whose matrix shows little or no peroxidase staining. These observations are interpreted as evidence that (a) catalase is capable of entering preexisting microbodies without traversing the cisternae of the rough endoplasmic reticulum or the Golgi apparatus, and that (b) the ribosomal staining is probably not cytochemical diffusion artifact and may represent a localized site of synthesis or activation of catalase.

The synthesis and turnover of rat liver peroxisomes. 3. The size distribution of peroxisomes and the incorporation of new catalase

Rat liver peroxisomes have been separated according to size by zonal sedimentation. A method is described for calculating the size of the particles from their final position in the gradient. Peroxisomes seem biochemically homogeneous throughout their size distribution. 3 hr after injection of tritiated leucine, the specific radioactivity of catalase is the same in peroxisomes of different sizes, and it remains so for up to 1 wk after administration of the precursor. This observation rules out the possibility that peroxisomes have an extended period of independent growth. If individual particles maintain an independent existence, they must be formed very rapidly. The other possible explanation is that peroxisomes exchange material within the liver cell.

New observations on microbodies. A cytochemical study on CPIB-treated rat liver

The liver of male rats has been studied after CPIB stimulation by using the peroxidase reaction for localizing catalase in hepatic cells. CPIB administration leads to an increase in the number of microbodies, and it is suggested that one mechanism by which microbody proliferation occurs is a process of fragmentation or budding from preexisting microbodies. Reaction product was observed not only within the microbody matrix, but outside the limiting membrane of the microbody and in association with ribosomes of adjacent rough endoplasmic reticulum. This localization of reaction product is interpreted as evidence that catalase after synthesis on rough endoplasmic reticulum may accumulate near microbodies and may be transferred directly into these organelles without traversing the cisternae of the endoplasmic reticulum or Golgi apparatus.