Biomedical subjects

C Okoh

Publications and source records attributed to C Okoh.

4 recordsLinked to original sources

PubMed1993

Carotenoid-protein complexes.

This chapter provides an updated report of carotenoprotein-related research. Very few carotenoproteins have been purified; however, their presence in aqueous extracts may be indicated by spectroscopic evidence. Carotenoproteins have been isolated, purified, and characterized from the ectoderm, exoskeleton, eggs, and ovaries of marine invertebrates, especially crustaceans. Water-soluble and detergent-soluble carotenoid-protein complexes have also been isolated from the cytoplasmic membrane of some cyanobacteria, Mangifera indica, and carrots. Recently, we have been able to partially purify a beta-carotene-protein complex from fresh livers of rats fed beta-carotene. Studies are currently in progress to purify and characterize the protein. This is the first successful isolation of a vertebrate carotenoprotein. The isolation of carotenoproteins is generally by standard techniques of protein chemistry. Purification, crystallization of the complex, and reconstitution of apoprotein and carotenoid components have been achieved for some crustacean carotenoproteins. The complex is very sensitive to bright light and to temperatures above that of refrigeration. However, it is best preserved in solutions of high ionic strength or as a precipitate in strong ammonium sulfate solutions.

Animals↗

PubMed1993

Enzymatic conversion of all-trans-beta-carotene to retinal.

Enzymatic conversion of all-trans-beta-carotene to retinal by a partially purified enzyme from rabbit, rat, and human neonatal intestinal mucosa has been demonstrated. The enzymatic product was characterized based on the following evidence. First, the product gave rise to its O-ethyl oxime by treatment with O-ethylhydroxylamine with an absorption maximum at 363 nm in ethanol characteristic of authentic retinal (O-ethyl) oxime. High-performance liquid chromatography of this derivative yielded a sharp peak with a retention time of 7.99 min, corresponding to the authentic compound. The enzyme blank and boiled enzyme blank failed to show any significant HPLC peaks corresponding to retinal (O-ethyl) oxime or retinal or retinol. Second, the mass spectrum of the O-ethyl oxime of the enzymatic product was identical to that of authentic retinal (O-ethyl) oxime (m/z 327, 45%; m+ and m/z 282, 100%, methoxy). Third, the 14C radioactivity persisted to constant specific activity even after repeated crystallization of the retinal (O-ethyl) oxime isolated from the enzyme reaction with purified beta-[14C]carotene. Fourth, the enzymatic product exhibited an absorption maximum at 370 nm in light petroleum characteristic of authentic retinal. Furthermore, it was reduced by horse liver alcohol dehydrogenase to retinol with an absorption maximum at 326 nm in light petroleum. This retinol was enzymatically esterified to retinyl palmitate by rat pancreatic esterase with a retention time of 10 min on HPLC, corresponding to authentic retinyl palmitate. Thus, the enzymatic product of beta-carotene cleavage by the partially purified intestinal enzyme has been unequivocally confirmed to be retinal. Similarly, enzymatic conversion of all-trans-beta-carotene to retinal by an intestinal mucosal enzyme from autopsy samples of human neonates has also been demonstrated. Based on the observed activities among intestinal samples from 12 premature infants, the BCC enzyme activity ranged from 3.3 to 1210 pmol/mg mucosal protein/hr. However, the observed activities in the human autopsy samples may be markedly underestimated, presumably because of marked loss of enzyme activity from the time of death to the time of assay. Therefore, the true activity of the enzyme can be assessed only after the extent of the loss of its activity on storage of the human samples can be accurately measured. Nonetheless, the demonstration of BCC enzyme activity in human neonates shows that beta-carotene may be an important source of vitamin A nutrition during gestation.

Animals↗

PubMed1993

Effects of chronic ethanol on enzymes regulating sialylation and desialylation of transferrin in rats.

Transferrin is N-glycosylated glycoprotein and plays an important role in iron transport from sites of absorption and storage to sites of utilization. Chronic ethanol alters the normal microheterogeneity pattern of transferrin as a consequence of changes in the sialic acid content. However the underlying basis of this change in sialic acid contents of transferrin in alcohol abuse remains unclear. We have undertaken this study in order to investigate the effects of chronic ethanol in rats with respect to the hepatic rate of (i) transferrin synthesis based on labeled leucine incorporation, (ii) the incorporation of labeled N-acetyl mannosamine (NAM) into sialic acid residues of transferrin, and (iii) roles of specific sialyltransferase and sialidase at hepatic subcellular level. The results showed no significant difference in the incorporation of labeled leucine into transferrin at all levels between the control and ethanol group, whereas the incorporation of NAM into transferrin was significantly decreased by 84% (p < 0.001) both at the whole cell and Golgi level. Thus, the incorporation of labeled NAM relative to the incorporation of labeled leucine into hepatic transferrin was significantly decreased by 86% (p < 0.001) in chronic ethanol-treated animals as compared with the controls both at the whole cell golgi levels. These data are further supported by our finding of concomitant decrease in the activity of beta-galactoside alpha 2,6-sialyltransferase by 58% (p < 0.01) in ethanol-treated rats as compared with control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcoholism↗

PubMed1984

Opsonization of pneumococci by whole serum from sickle cell disease patients.

An in vitro opsonic activity test was developed to measure the ability of whole serum from sickle cell disease patients to enhance the phagocytosis of Streptococcus pneumoniae by normal white blood cells. At the 30- and 60-minute incubation time periods, there was a 2- to 3-log reduction in the number of colonyforming units of S pneumoniae with both normal and sickle cell serum indicating opsonization of the organisms. However, the reduction in colony-forming units was significantly greater with normal than with sickle cell serum at both time periods (P <.0005 and P <.025 for the 30- and 60-minute time intervals, respectively). The sickle cell sera used in this assay were obtained from pediatric patients (age range, 1 to 15 years) and from adults (age range, 16 to 30 years). Based on this assay, sera from the adult sickle cell patients had a lower mean opsonic activity than that of the pediatric group. The significance of the lower opsonic activity in the adults with sickle cell disease is unknown and requires additional investigation.

Adolescent↗