Substrate-Induced Stability of Glyceraldehyde 3-Phosphate Dehydrogenase from Mung Beans (Vigna radiata L.)

Time-dependent thermal inactivation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) present in the extract of mung beans at different periods of germination showed biphasic kinetics in the 12-h germinated seeds but single exponential decay at 24 h of germination. The glyceraldehyde 3-phosphate (G-3-P) concentration in the deproteinated extracts was found to increase with period of germination up to 36 h, parallel to that of GAPDH activity. G-3-P was found to offer protection of the enzyme against thermal inactivation and trypsin digestion. It is suggested that accumulation of G-3-P in germinating mung beans may be of physiological significance and it might offer protection to the enzyme in vivo against thermal inactivation and proteolysis.     

Studies on the mechanism of uptake of low density lipoprotein-proteoglycan complex in macrophages

Earlier, we (Vijayagopal, P. et al. (1988) Biochim. Biophys. Acta 960, 210) showed that mouse peritoneal macrophages metabolize low density lipoprotein (LDL)-proteoglycan complex by a receptor pathway distinct from the acetyl-LDL receptor. Further studies were conducted to probe further into the mechanism of LDL-proteoglycan complex uptake by macrophages. Both 125I-methyl-LDL-proteoglycan complex and 125I-LDL-proteoglycan complex were taken up and degraded by the cells to the same extent. Similarly, the ability of these ligands to stimulate cholesteryl ester synthesis was also indistinguishable. These results rule out the possibility of apoB,E receptor involvement in the uptake of LDL-proteoglycan complex in macrophages. Sodium fluoride, cytochalasin D and aggregated LDL inhibited degradation of the complex by 24%, 26% and 28%, respectively, indicating that phagocytosis is only a minor pathway for the uptake. Both binding and degradation of the complex were not inhibited by excess hyaluronic acid suggesting that ligand recognition was not through hyaluronic acid binding sites. As compared to acetyl-LDL, the cellular degradation of LDL-proteoglycan complex was retarded. Macrophages exhibited a rapid stimulation of [3H]inositol trisphosphate (IP3) release and diacylglycerol production when incubated with LDL-proteoglycan complex. Furthermore, pertussis toxin produced a 62% inhibition of LDL-proteoglycan complex mediated IP3 release, suggesting that LDL-proteoglycan complex metabolism in macrophages is dependent upon the G-protein coupled signal transduction mechanism. These results show that receptor mediated endocytosis plays a major role in the metabolism of LDL-proteoglycan complex in macrophages.     

Plant regeneration via somatic embryogenesis in creeping bentgrass (Agrostis palustris Huds.)

We have established a high-frequency plant regeneration system via somatic embryogenesis from mature seeds of creeping bentgrass (Agrostis palustris Huds). The effects of 2,4-dichlorophenoxyacetic acid (2,4-D), 3.6-dichloroo-anisic acid (dicamba) and 6-benzyladenine (BA) on callus formation and embryogenesis were evaluated. Callus produced on the Murashige and Skoog (MS) (1962) medium containing 2,4-D had low embryogenic potency. In the presence of 30 M dicamba, addition of 2.25 to 9 M BA significantly enhanced embryogenic callus formation over dicamba alone. Optimum frequency of somatic embryogenesis was achieved on MS basal medium containing 30 M dicamba and 2.25 M BA. Over 80% of somatic embryos germinated and formed plantlets on half-strength MS basal medium. These plantlets grew normally in the greenhouse.Abbreviations MS Murashige and Skoog medium - 2,4-D 2,4-dichlorophenoxyacetic acid - BA 6-benzyladenine - dicamba 3, 6-dichloro-o-anisic acid     

Dietary hexachlorocyclohexane induced changes in blood and liver lipids in albino mice.

Dietary intake of technical hexachlorocyclohexane (HCH) by albino mice for 2 weeks (at 400 and 800 ppm) resulted in hyperlipemia. Significant increase in triglycerides, phospholipids and cholesterol fractions of blood was observed in these animals. Dietary intake of gamma-isomer of HCH for 2 weeks (at 200 ppm) did not have any effect on blood lipid profile, but at 400 ppm level produced higher contents of phospholipids and cholesterol. The hepatomegaly produced by dietary technical HCH or gamma-HCH was not accompanied by fatty metamorphosis of liver. Hypertriglyceridemia caused by HCH was accompanied by lower triglyceride levels in liver, suggesting a possible higher rate of secretion from liver.     

Inhibition of RNA-dependent DNA polymerase activity of oncornaviruses by caffeine.

Caffeine was found to inhibit RNA-dependent DNA polymerase activity of Rauscher leukemia virus when endogenous viral RNA and poly(rA)·(dT)_12–18 were used as templates. Similar results were also obtained with purified RNA-dependent DNA polymerase (deoxynucleoside triphosphate; DNA nucleotidyl transferase; EC 2.7.7.7) from avian myeloblastosis virus (AMV) utilizing 70S and 35S RNA of AMV, poly(rA)·(dT)_12–18, globin mRNA and activated calf thymus DNA as templates. The “caffeine effect” was evident only when it was present during the initiation of polymerization reaction. Increasing the template concentration in the reaction mixture partly reversed the effect of caffeine. Of the analogs of caffeine tested, only theophylline inhibited AMV DNA polymerase, whereas aminophylline showed no effect.     

Human psychophysics: Functional interpretation for contrast sensitivity versus spatial frequency curve

The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.This research was conducted at Yale University, Department of Ophthalmology and Visual Science, New Haven, Connecticut, USA, throughout which period A.W.S. was a John Simon Guggenheim fellow     

A note on the Mulder-Landsmeer phenomenon.

Mulder-Landsmeer phenomenon (inability to activiely straighten the interphalangeal joints fully when the metacarpophalangeal joint of a finger is passively held in maximal hyperextension) was confirmed in the normally hypermobile South Indian fingers. A powerful but limited de-extension of the proximal phalanx was noticied, in normagers, during completion of interphalangeal extension when the metacarpophalangeal joint was passively held in maximal hyperextension...