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Biomedical subjects

B A Cooper

Publications and source records attributed to B A Cooper.

At least 91 records · Page 5Linked to original sources
PubMed1975

Incorporation and metabolic conversion of cyanocobalamin by Ehrlich ascites carcinoma cells in vitro and in vivo.

1. Cyano [57 Co] cobalamin bound to murine transcobalamin, associates with Ehrlich ascites carcinoma cells. Association was found to be dependent on temperature, and to require between 7.2 - 10-5 and 2 - 10-4 M ionized calcium. 2. Association was blocked by vinblastine and colchicine, but not cytochalasin, suggesting that microtubules may be involved in this phenomenon. 3. Although irreversible association of radioactivity with cells was observed within minutes, appearance of significant radioactivity associated with the intracellular B12 binder, and conversion of cyanocobalamin to methyl- and 5'deoxyadenosylcobalamin required more than 18 h of incubation. 4. A pool of free vitamin B12 was found in cell extracts. This was composed of metabolically-active cobalamins characteristic of the interior of the cell, and not of cyanocobalamin recently incorporated. 5. Incorporation of 57Co-labelled vitamin B12 by these cells involves two major processes: a rapid irreversible association of transcobalamin-B12 complex following reaction with a presumably calcium-dependent receptor, and a much later entry of vitamin into the cytoplasm to become exposed to enzymes and associated with an intracellular binder.

Animals↗
PubMed1974

Solubilized receptor for intrinsic factor-Vitamin B12 complex from guinea pig intestinal mucosa.

the absorption of vitamin B(12) in many animals requires its prior association with intrinsic factor (IF) and attachment to a specific receptor in the intestine. Employing Triton X-100, we have solubilized from guinea pig ileum a factor that binds intrinsic factor-vitamin B(12) complex (IF-B(12)). This binding factor was soluble to the extent that it was not sedimented by centrifugation at 100,000 g for 1 h and was small enough to enter the included volume of a Sepharose 4-B column. Furthermore, the ileal extract contained no microfine particles of membrane upon electron microscopic search. When a portion of the extract was incubated with a mixture of gastric juice and (57)Co-labeled vitamin B(12), a portion of the radioactivity was excluded from a Sephadex G-200 column. When gastric juice from a patient with a congenital abnormality of IF that prevented its binding to intestine was substituted for normal human gastric juice, radioactivity was not excluded from the gel, indicating failure of this abnormal IF-B(12) to bind to the intestinal extract. These data suggested the presence of a specific binder of IF-B(12) in the ileal mucosal extract. The reactions of normal IF-B(12) with the solubilized binding factor and with the membrane-bound "receptor" had several characteristics in common, including calcium dependence, temperature independence, and pH optimum near neutral. Extracts from the distal intestine showed more activity than did those from the proximal. The solubilized binding facter seemed specific for IF-B(12) in that it was not blocked by prior incubation with excesses of either free vitamin B(12) or IF. Binding activity of the extract was decreased by incubation at pH 2.0, by heating to 56 degrees C, and by incubation with chymotrypsin and dithiothretiol. Incubation with trypsin, neuraminidase, and sulphydryl blockers did not affect it. The Triton X-100 extract of guinea pig ileal mucosa contains a specific binding factor that probably is the receptor for IF-B(12). This appears to be a protein with function dependent on peptide and disulphide linkages.

Animals↗
PubMed1973

Superiority of simplified assay for folate with Lactobacillus casei ATCC 7469 over assay with chloramphenicol-adapted strain.

Direct assay of serum folate by mixing serum with a mixture of L. casei and medium without autoclaving was found to provide serum folate results similar to those by extraction of serum with heat. This procedure was found more reliable than that using the same technique with chloramphenicol and a strain of L. casei adapted to grow in this material. A portion of apparent folate activity assayed in haemolysates by such direct assay was found to be due to material other than folate. It is recommended that heat extraction of haemolysates be continued for determination of whole blood folate, or that an additional standardization of technique be included if direct assay is used.

Biological Assay↗
PubMed1971

Folates in plasma and bile of man after feeding folic acid--3H and 5-formyltetrahydrofolate (folinic acid).

During the 1st hr after feeding folic acid-(3)H ((3)H-PteGlu) to fasting human volunteers, plasma S. faecalis and (3)H activity were elevated to an equivalent degree, whereas after this, the (3)H activity exceeded S. faecalis activity, which suggests gradual conversion of folic acid-(3)H to methyltetrahydrofolate-(3)H (5-CH(3)H(4) PteGlu). The increase of L. casei activity exceeded the increase of S. faecalis and (3)H activity, which is consistent with flushing of endogenous methyltetrahydrofolate from the tissues by the administered folic acid-(3)H. Feeding of 5-formyltetrahydrofolate (+/-5CHOH(4)PteGlu) produced a large increase of plasma L. casei activity and only a slight increase of S. faecalis and P. cerevisiae activity, which is consistent with very rapid conversion of folinic acid to methyltetrahydrofolate. Bile folate concentration determined microbiologically was 2.3-9.8 times plasma folate. 40-80% of the bile folate was S. faecalis-active and 20-35% P. cerevisiae-active. Chromatography of bile folates on TEAE-cellulose showed several folates including four tentatively identified as 10-formyltetrahydrofolate (10-CHO-H(4)PteGlu), 10-formylfolate (10-CHO-PteGlu), and/or 10-formyldihydrofolate (10-CHOH(2)PteGlu), methyltetrahydrofolate, and possibly a triglutamate folate. After folate ingestion bile folate concentration increased rapidly. The distribution of bile folates measured by microbiological assay was similar after either folic or folinic acid feeding. Most of the (3)H label of folic acid-(3)H appeared in the biological folates of bile rather than in the folic acid fraction, which shows that the administered folic acid was rapidly transformed to other folates. Folate polyglutamate deconjugating enzyme activity was found to be much less than in serum. Polyglutamates of the type found in yeast were not found in bile. It is suggested that biliary folate may reflect the hepatic intracellular oligoglutamate folate pool rather than the folate as it appears in the hepatic portal blood.

Bile↗