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Biomedical subjects

P H Koo

Publications and source records attributed to P H Koo.

9 recordsLinked to original sources
PubMed1992

Inhibition of nerve growth factor-stimulated neurite outgrowth by methylamine-modified alpha 2-macroglobulin.

alpha 2-Macroglobulin (alpha 2M) is a rather ubiquitous protein in extracellular spaces of mammals. It is an inhibitor of endopeptidases, can be modified by aliphatic amines, and combines with a number of hormones/cytokines such as beta-nerve growth factor (NGF) [Koo PH, Stach RW (1989): J Neurosci Res 22:247]. The objective of this study is to compare the NGF-binding properties of methylamine-modified human alpha 2M (MA-alpha 2M) versus normal alpha 2M and their effects on the biological activity of NGF and neurite extension by embryonic chicken dorsal root ganglia. As determined by gel filtration, polyacrylamide gel electrophoresis, and equilibrium binding studies, these two forms of alpha 2M are similar in their binding affinities, with MA-alpha 2M binding about twice as much NGF as normal alpha 2M. Both normal alpha 2M and MA-alpha 2M combine noncovalently with NGF, and prior modification of alpha 2M is unnecessary for the binding to occur. In contrast to normal alpha 2M, MA-alpha 2M potently inhibits the biological activity of NGF and exerts a dose-dependent inhibition on the NGF-stimulated neurite outgrowth by embryonic chicken dorsal root ganglia in culture. The inhibitory effect of MA-alpha 2M can be overcome by higher NGF concentrations, but is irreversible at lower NGF concentrations. Trypsin-modified alpha 2M combines covalently and noncovalently with more NGF than normal alpha 2M but has very little neurite inhibitory activity. The mechanism of inhibition by MA-alpha 2M is discussed.

Animals↗
PubMed1989

Interaction of nerve growth factor with murine alpha-macroglobulin.

The murine nerve growth factor, when injected i.v. or, combined in vitro with plasma, was found largely associated with the mouse alpha-macroglobulin (a homologue of human alpha 2-macroglobulin). The nerve growth factor-alpha-macroglobulin complex produced is sufficiently stable to resist separation by gel filtration in 1.0 M sodium chloride, polyacrylamide gel electrophoresis, and immunoprecipitation by antibodies against alpha-macroglobulin. As determined by equilibrium binding studies and computer generated Scatchard analysis, alpha-macroglobulin apparently possesses two types of binding sites with the apparent dissociation constants of 1.2 x 10(-6) and 2.9 x 10(-9) M, respectively, saturable by 3.7 and 0.03 moles of nerve growth factor. Hence, about one mole of nerve growth factor is bound to each of the four subunits of alpha-macroglobulin. Nerve growth factor can be readily dissociated from alpha-macroglobulin in sodium dodecyl sulfate gel electrophoresis in the absence of a reductant. Procedures that affect the proteinase-binding or methylamine- activities of alpha-macroglobulin do not affect the binding of nerve growth factor, and the binding is unaffected by the presence of zinc ions or EDTA. Hence, nerve growth factor is noncovalently associated with alpha-macroglobulin at a site separate from that of the proteinase-, methylamine-, and zinc-binding sites of alpha-macroglobulin. Mouse alpha-macroglobulin can protect the nerve growth factor from inactivation by trypsin. Even in the presence of trypsin, alpha-macroglobulin-nerve growth factor complexes still can stimulate the neurite outgrowth by dorsal root ganglia of 9-day-old chicken embryos. Since alpha-macroglobulin can specifically and noncovalently carry nerve growth factor, one important role of this alpha-macroglobulin in the circulation and extracellular spaces may be to protect the nerve growth factor from proteinase inactivation.

Animals↗
PubMed1987

Mouse alpha-macroglobulin. Structure, function and a molecular model.

Mouse alpha-macroglobulin (M-AMG) is believed to be a functional homologue of human alpha 2-macroglobulin (h-alpha 2M). The subunit composition, the tryptic cleavage pattern before and after methylamine incorporation and the two-dimensional tryptic-peptide mapping, however, indicate that these two proteins are structurally distinct. M-AMG is composed of two major types of polypeptides (Mr 163,000 and 35,000) together with a minor polypeptide (Mr 185,000), whereas h-alpha 2M has only one type of polypeptide (Mr 185,000). After incorporation of methylamine, there is no change in the normal tryptic-cleavage pattern of M-AMG; however, tryptic cleavage of h-alpha 2M is severely retarded [Hudson & Koo (1982) Biochim. Biophys. Acta 704, 290-303]. The N-terminal sequence of the 163,000-Mr polypeptide of M-AMG shows sequence homology with the N-terminal sequence of h-alpha 2M. The amino acid compositions of M-AMG and its two major polypeptide chains are compared. Thermal fragmentation studies show that the 163,000-Mr polypeptide is broken down into 125,000-Mr and 29,000-Mr fragments. Trypsin-binding studies show that M-AMG can bind two molecules of trypsin/molecule. Inactivations of the trypsin-binding property of M-AMG and h-alpha 2M with methylamine show similar kinetics of inhibition at 4 degrees C. A structural model of M-AMG is proposed, based on accumulated data.

Amino Acids↗
PubMed1974

Specificity of antibodies: primary structural basis of hapten binding.

The primiary structure of the 83 residues of the NH(2)-terminus of the V(II), region was determined for each of three different antibodies to hapten which were produced in inbred guinea pigs. Each antibody had a different and distinctive primary structure within each of the two "hypervariable" regions (Hv1 and Hv2) included in the analyzed part of the variable region of the heavy chain. The sequences of Hvl and Hv2 in the three antibodies were either unique or of restricted variability compared with those of "normnal" immunoglobulin G2. Further implication of Hv1 and Hv2 in contributing to ligand-binding specificity of antibodies came from the placement of residues modified by affinity labeling reagents in these hypervariable regions.

Amino Acid Sequence↗
PubMedDate not supplied

Antitumor effect of novel silatranes on renal cell carcinoma in mice.

The effect of several novel silatrane derivatives on the growth of syngeneic renal cell carcinoma (RENCA) in BALB/c mice and the survival rate of the animals were evaluated. The RENCA-bearing animals were treated subcutaneously and weekly with either a water-insoluble or a water-soluble derivative. The silatrane-treated animals were either free of palpable tumors or developed tumors much more slowly in comparison with the control animals without silatranes. The treated animals as a whole also died of tumor at much slower rates. Attempts to use higher silatrane dosages to achieve better curative effects were hampered by the toxicity of these compounds.

Animals↗
PubMedDate not supplied

Natural cytotoxins in human plasma: isolation and characterization of phospholipids associated with cytotoxic lipoproteins.

Most of the heat-stable natural cytotoxins in normal human plasma were fractionated by gel filtration into two active fractions: the alpha 2-macroglobulin (alpha 2M) and pre-alpha 2M pools. The pre-alpha 2M pool also appeared to contain most of the phospholipids in human plasma. The pre-alpha 2M pool was further purified by ultracentrifugation and was shown to contain cytotoxic lipoproteins that represented most of the cytotoxin activity in the pool. The phospholipids associated with the pre-alpha 2M pool and purified lipoproteins resisted dialysis in a buffered saline but were extractable by organic solvents. Two major phospholipids (compounds A and B) were extracted, and both exhibited cytotoxic activities. Compound A exerted dose-dependent, species-nonspecific growth-inhibitory or cytotoxic effects on tumor cells in vitro. It was a lecithin-like compound but was more potent than any of the lecithin standards tested, except for a polyunsaturated lecithin. The possibilities that certain lecithin-like compound(s) contribute significantly to the cytotoxic activity of the lipoproteins and their role in cancer resistance are discussed.

Animals↗