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Biomedical subjects

P Bornstein

Publications and source records attributed to P Bornstein.

At least 181 records · Page 10Linked to original sources
PubMed1975

Interchain disulfide bonds in procollagen are located in a large nontriple-helical COOH-terminal domain.

Tadpole collagenase (EC 3.4.24.3) cleaved chick cranial bone procollagen into two triple-stranded fragments, PCA and PCB. Only PCB, with an estimated molecular weight of about 60,000 for each component chain after reduction, was found to contain interchain disulfide bonds. The analogous cleavage of collagen is known to produce a large NH2-terminal fragment with a molecular weight of 70,000 for each chain and a small COOH-terminal fragment containing chains of about 25,000 molecular weight. Since PCB was too small to represent the product NH2-terminal to the site of collagenase cleavage, localization of interchain disulfide bonds to a COOH-terminal domain in procollagen was indicated. This assignment was conformed by Dintzis-type short-term labeling experiments. Procollagen obtained by acid extraction of bone lacked the COOH-terminal disulfide-bonded domain. The findings support a model for procollagen consisting of three proalpha chains each containing nonhelical NH2-terminal extensions of 20,000 molecular weight and COOH-terminal extensions of about 35,000 molecular weight, the latter linked by interchani disulfide bonds.

Animals↗
PubMed1975

Location of procollagen in chick corneal and tendon fibroblasts with ferritin-conjugated antibodies.

Three distinct antiprocollagen preparations were characterized and used in immunocytochemical staining of chick embryo corneal and tendon cells. The several ferritin-conjugated antibody preparations permitted similar location of procollagen in the cisternae of the rough endoplasmic reticulum and in Golgi elements in both cell types. The ability to demonstrate and interpret specific ferritin staining was dependent on the extent of membrane breakage in each of those organelles, coupled with adequate retention of cell morphology. Corneal fibroblasts appeared to suffer more extensive intracellular membrane damage under controlled conditions of homogenization than tendon fibroblasts, facilitating the identification of procollagen in Golgi vacuoles of these cells. None of the labeled material appeared to by cytoplasmic in origin since ferritin was observed in the cytoplasm only in the vicinity of Golgi elements that were extensively broken. This study extends previous immunological evidence for the presence of procollagen in the Golgi complex and calls attention to the problems to be encountered in locating the antigen in small Golgi vesicles and lamellae.

Animals↗
PubMed1974

Effects of antimicrotubular agents on the secretion of collagen. A biochemical and morphological study.

Embryonic chick cranial bone was cultured in the presence of the antimicrotubular agents, colchicine and vinblastine, and with a number of other compounds known from previous studies to affect the cellular handling of collagen. Secretion of procollagen, quantitated by light microscope autoradiography, was correlated with the extent of conversion of procollagen to collagen and with rates of collagen and noncollagen-protein synthesis. Colchicine inhibited procollagen secretion and conversion to collagen and specifically inhibited collagen synthesis. Cells exposed to colchicine revealed an increased number of dilated Golgi-associated vacuoles and vesicles, some of which contained parallel aggregates of filamentous structures. These observations suggest that the pathway of at least a fraction of procollagen secretion by osteoblasts includes the Golgi complex. Disruption of microtubules may interfere with the movement of Golgi-derived vesicles, and the resulting accumulation of collagen precursors in the Golgi complex may lead secondarily to an inhibition of synthesis. Although vinblastine also inhibited both procollagen secretion and conversion to collagen, the observed reduction in general protein synthesis and striking changes in the ultrastructure of the rough endoplasmic reticulum complicated interpretation of the effects. Interpretation of the effects of cytochalasin B was limited by the finding that the cellular response in cranial bone was markedly heterogeneous and that, contrary to some previous reports, the drug caused an inhibition in the incorporation of radiolabeled amino acids into both collagen and noncollagen protein.

Animals↗
PubMed1972

Procollagen: conversion of the precursor to collagen by a neutral protease.

An enzymatic activity (procollagen peptidase), capable of converting the biosynthetic precursor procollagen to collagen at neutral pH, has been identified in rat and chick calvarial bone. Limited proteolysis of procollagen with chymotrypsin resulted in a similar transformation. The activity in bone can be demonstrated in vitro despite inhibition of new collagen synthesis by cycloheximide. Preservation of the collagen precursor in preparations extracted with acetic acid results from inhibition of the enzymatic activity at low pH.

Animals↗