Intermolecular specificity of pancreatic lipase in the lipolysis of triacylglycerols containing phytanic acid.

Diffusional effects on two-substrate enzymic reactions mainly depend on the relative affinities of the enzyme for its two substrates. With two substrates of widely different affinities, diffusional limitations increase and decrease the half-maximal-activity concentration of the high-and low-affinity substrate respectively.     

Tryptophan pyrrolase in haem regulation. Experiments with administered haematin and the relationship between the haem saturation of tryptophan pyrrolase and the activity of 5-aminolaevulinate synthase in rat liver.

1. Administration of haematin to rats decreases 5-aminolaevulinate synthase activity in whole liver homogenates. 2. An inverse relationship between this decrease and the increase in saturation of apo-(tryptophan pyrrolase) with haem is observed during the initial phase of treatment with haematin. 3. Significant changes in both functions are caused by a 1 mg/kg dose of haematin, whereas the maximum effects are achieved by the 5 mg/kg dose. 4. Prevention by allopurinol of the conjugation of exogenously administered haematin with apo-(tryptophan pyrrolase) renders this haem available for further repression of 5 aminolaevulinate synthase. 5. The various aspects of the relationship between synthase activity and the haem saturation of tryptophan pyrrolase are discussed.     

Two small virus-specific polypeptides are produced during infection with Sindbis virus.

We have identified and characterized two small virus-specific polypeptides which are produced during infection of cells with Sindbis virus, but which are not incorporated into the mature virion. The larger of these is a glycoprotein with an approximate molecular weight of 9,800 and is found predominantly in the medium of infected cells. Three independent lines of evidence demonstrate conclusively that this 9,800-dalton glycoprotein is produced during the proteolytic conversion of the precursor polypeptide, PE2, to the virion glycoprotein E2. This small glycoprotein is therefore analogous to the virion glycoprotein E3 of the very closely related alphavirus, Semliki Forest virus. The 9,800-dalton glycoprotein of Sindbis virus, unlike the E3 glycoprotein of Semliki Forest virus, is not, however, present in the viral particle. The other virus-specific polypeptide is 4,200 daltons in size, does not appear to be a glycoprotein, and is neither incorporated into the mature virus nor released into the culture medium. The gene for this small polypeptide is present in the viral 26S mRNA (the mRNA which encodes all the viral structural polypeptides) and appears to be located in the portion of the mRNA which encodes the two viral glycoproteins. The possibility that this 4,200-dalton polypeptide functions as a signal peptide during the synthesis of the viral membrane glycoproteins is discussed.     

Effect of transient ischemia on monoamine levels in the cerebral cortex of gerbils

Abstract— Cortical monoamine changes during ischemic episodes of varied duration and their sequence of changes following cerebral reperfusion were studied in the gerbil. Forty-one percent of 280 animals exhibited signs of cerebral hemispheric ischemia (stroke) after unilateral common carotid artery occlusion. Norepinephrine (NE) levels decreased after 60 min in the occluded hemisphere of stroked animals but dopamine (DA) levels were unaltered. S-Hydroxytryptamine (5-HT) levels became bilaterally reduced in both stroked and non-stroked animals as soon as S min after occlusion. Upon reperfusion after periods of 30 or 60 min of occlusion there was a bilateral rebound increase of cortical NE and DA levels to well above control values in stroked and non-stroked animals. 5-HT levels remained reduced in both groups. Results suggest disorder of monoamine metabolism in ischemic brain which persists during the early reperfusion period, perhaps contributing to deficits in neurological function. Monoamine changes in contralateral non-ischemic hemispheres both during the occlusion and reperfusion periods are thought further evidence of diaschisis.     

The two mammalian mitochondrial stress proteins, grp 75 and hsp 58, transiently interact with newly synthesized mitochondrial proteins.

In mammalian cells, two of the so-called heat shock (hsp) or stress proteins are components of the mitochondria. One of these, hsp 58, is a member of the bacterial GroEL family, whereas the other, glucose-regulated protein (grp) 75, represents a member of the hsp 70 family of stress proteins. Owing to previous studies implicating a role for both the hsp 70 and GroEL families in facilitating protein maturation events, we used the method of native immunoprecipitation to examine whether hsp 58 and grp 75 might interact with other proteins of the mitochondria. In cells pulse-labeled with [35S]-methionine, a significant number of newly synthesized mitochondrial proteins co-precipitated with either hsp 58 or grp 75. Such interactions appeared transient. For example, providing the pulse-labeled cells a subsequent chase period in the absence of radiolabel resulted in a reduction of co-precipitating proteins. If the pulse-chase labeling experiments were performed in the presence of an amino acid analogue, somewhat different results were obtained. Specifically, although many of the newly synthesized and analogue-containing proteins again were observed to co-precipitate with grp 75, the interactions did not appear transient, but instead were stable. Under steady-state labeling conditions, we also observed a portion of hsp 58 and grp 75 in an apparent complex with one another. On addition of ATP, the complex was dissociated. Accompanying this dissociation was the concomitant autophosphorylation of grp 75. On the basis of these observations, as well as previous studies examining the structure/function of the hsp 70 and GroEL proteins, we suspect that both hsp 58 and grp 75 interact with and facilitate the folding and assembly of proteins as they enter into the mitochondria.     

Evidence that heat shock protein-70 associated with progesterone receptors is not involved in receptor-DNA binding.

In the absence of hormone, human progesterone receptors (PR) are recovered in the cytosolic fraction of cell lysates as a multimeric complex containing the steroid-binding polypeptide, heat shock protein-90 (hsp90), and heat shock protein-70 (hsp70). Activated forms of human PR that acquire the ability to bind to DNA are dissociated from hsp90, but retain association with hsp70. The present study has examined whether associated hsp70 has a function in receptor-DNA binding. When activated PR was bound to specific target DNA in a gel shift assay, no hsp70 was detectable in the PR-DNA complex, as evidenced by the failure of several antibodies to hsp70 to affect the mobility or the amount of complexes. To determine whether hsp70 might indirectly influence DNA-binding activity, we have examined the effect of hsp70 dissociation on PR-DNA-binding activity. Dissociation was achieved either by treatment of immunoaffinity-purified immobilized PR complexes with ATP or by the binding of PR complexes to ATP-agarose, followed by elution with high salt. Under both conditions, dissociation from hsp70 neither enhanced nor impaired the ability of PR to bind to specific DNA. These results suggest that hsp70 is not involved in PR binding to DNA, either directly by participating in DNA binding or indirectly by modulating PR-DNA-binding activity. This implies that hsp70 functions at an earlier stage in the receptor activation pathway. Consistent with the known involvement of hsp70 in stabilizing unfolded states of other target proteins, we propose that hsp70 may assist in nuclear transport of PR or in assembly-disassembly of the 8-10S multimeric complex.     

Inhibition of tumor cell invasion by verapamil.

Verapamil, a calcium channel antagonist, inhibits murine B16 melanoma and colon adenocarcinoma C26 tumor metastasis by altering platelet aggregation [Tsuruo, T., et al. (1985) Cancer Chemother. Pharmacol., 14:30-33]. However, the role of calcium homeostasis in regulating several biochemical pathways implicated in other steps of the metastatic cascade suggests that calcium channel antagonists could also inhibit metastasis by other mechanisms. In this report, non-toxic doses of verapamil reversibly decreased human A375M and C8161 melanoma cell invasion and metastasis in a dose-dependent manner. Verapamil reduced cellular invasion and metastases by up to 96% (range 78-96%). Concomitantly, verapamil disrupts microtubule and microfilament organization and inhibits unidirectional cell migration but does not affect cellular adhesion to endothelial monolayers or reconstituted basement membranes. In addition, tumor cells treated with verapamil have a decrease in mRNA of type IV collagenase, a proteinase important in tumor cell degradation of basement membranes. Collectively, these data offer additional evidence regarding the mechanisms of action of verapamil as an anti-metastatic agent.     

Seasonal hair follicle activity and fibre growth in some New Zealand Cashmere-bearing goats (Caprus hircus)

Hair follicle activity and fibre growth were studied using histological sections from the skin of five adult feral does sampled every four weeks for 18 months. The main period of guard hair growth in primary follicles was from November to April. Secondary follicles grew fine, long, nonmedullated fibres (cashmere) from December to June. Shedding of these fibres from secondary follicles had commenced by July and cashmere was absent from the fleece by November. From September to December a subsidiary hair cycle occurred in many secondary follicles which produced minute (vellus) fibres, less than 2.4 mm in length. Some secondary follicles probably shed their cashmere fibres and remain quiescent over spring. Annual pelage changes were therefore achieved with one main growth period, although many secondary follicles underwent another brief hair cycle in spring.     

Metal concentrations in surficial sediments from hypersaline lakes,Australia

A major drawback to the use in aquaculture of members of the Eubranchiopoda from temporary pool environments is that their eggs do not hatch readily. An investigation of the factors influencing the hatching of eggs of the fairy shrimpStreptocephalus macrourus, showed that light was the only factor of those investigated that was obligatory for hatching. It was found that eggs which had not been desiccated hatched successfully in the presence of absence of adults, while those which had been desiccated showed a block in hatching initially, although this block deteriorated with time and after approximately two months the eggs which had been desiccated showed a similar hatching success to that of the non-desiccated eggs. Exposure of eggs to extremes of heat or cold before incubation did not influence the hatching success of the eggs significantly, but the temperature at which incubation took place was important. The optimal range lay between 14 °C and 20 °C. Eggs hatched and nauplii survived at dissolved oxygen tensions of below 0.5 mg 1^–1