MEMBRANE-ASSOCIATED PROTEOGLYCANS IN RAT TESTICULAR PERITUBULAR CELLS

Confluent testicular peritubular cells derived from immature rats were used to study membrane associated proteoglycans (PG). Peripheral mate rial (heparin releasable), membrane and intracellular material (Triton X-100 releasable) were collected, purified by anion exchange chromato graphy then characterized by gel filtration and by hydrophobic interac tion chromatography, followed by enzymatic digestion and chemical trea tment. The peripheral material was constituted of two populations of P G (K-av=0 and 0.10 on Superose 6 column), each containing both heparan sulfate proteoglycans (HSPG) and chondroitin proteoglycans (CSPG) and perhaps a hybrid PG (HSCSPG). These PG being not retained on an octyl Sepharose column, they were devoided of hydrophobic properties. The i ntegral membrane proteoglycans isolated on the basis of their hydropho bic properties represented 20% of the Triton X-100 releasable material , and were exclusively constituted of proteoheparan sulfate. There wer e no relationships between this membrane HSPG and the peripheral HSPG as evidenced by pulse chase experiments. The mode of intercalation of the hydrophobic HSPG in the cell membrane was studied. The majority of these macromolecules (80%) were sensitive to trypsin and only a minor proportion (20%) were sensitive to phosphatidylinositol specific phos pholipase C. Thus, about 80% of the hydrophobic HSPG were intercalated in the cell membrane by a hydrophobic segment of the core protein whe reas about 20% were associated with the cell membrane via a phosphatid ylinositol residue covalently bound to the core protein of the PG.