Walter F. Lever

Histochemical differentiation of peroxidase-mediated from tyrosinase-mediated melanin formation in mammalian tissues

SummaryPreincubation with the copper-chelator, sodium diethyldithiocarbamate (DDC) and the presence of catalase in the incubation media allowed an accurate and reproducible differentiation of the role of tyrosinase from that of peroxidase in the oxidation of tyrosine and dopa in melanocytes, mast cells and eosinophils. These studies indicated that mammalian peroxidase in melanocytes, mast cells and eosinophils can mediate the conversion of tyrosine to melanin in the presence of dopa co-factor, as well as the conversion of dopa to melanin. With the methods employed, there was no evidence that tyrosinase in the preparations studied had significant ability to mediate the oxidation of tyrosine to melanin (even in the presence of dopa co-factor), although there was abundant evidence that it can mediate the conversion of dopa to melanin. Mammalian peroxidase may have roles in initiating melanin synthesis and catechol amine synthesis in vivo.

LIPASES OF BLOOD AND TISSUES. III. PURIFICATION AND PROPERTIES OF PANCREATIC LIPASE.

Abstract Porcine pancreatic lipase has been purified 315-fold. The purified pancreatic lipase was homogeneous on ultracentrifugation and free-boundary electrophoresis. On starch-gel electrophoresis and DEAE chromatography, however, at least two components were present. The optimal pH for purified pancreatic lipase was 8.0–8.1. The eluates obtained after DEAE-cellulose column chromatography of purified pancreatic lipase were completely inactive. Addition of a heat-stable factor derived from pancreatic lipase to the inactive eluates restored the specific lipase activity to about 90% of its original value before DEAE chromatography.

Retinoic acid in psoriasis: its value for topical therapy with and without corticosteroids

Topical application of retinoic acid (RA, 0·1 and 0·3% in a cream base) in psoriasis over 3 weeks showed that low therapeutic effect and frequent irritation limit considerably its usefulness in this disease. Of twenty treated patients, six had irritation warranting discontinuation of therapy, thirteen showed improvement, but none cleared completely. However, the therapeutic value was increased and the incidence of irritation was reduced if corticosteroids (CO) were added to RA. Of twenty‐four patients treated with RA + CO, eighteen were improved and four cleared completely. Combined treatment seemed also to be more effective than CO alone in the same vehicle.

Peroxidase-dependent oxidation of tyrosine or dopa to melanin in neurons.

SummaryPeroxidase activity was demonstrated in guinea pig frontal lobe by histochemical methods, and was correlated with peroxidase-dependent enzymatic synthesis of melanin from tyrosine or dopa. Peroxidase activity and peroxidase-dependent melanin synthesis appeared to be mainly in lysosomes of neurons. These findings open the possibility that peroxidase may have a role in catecholamine, lipofuscin and neuromelanin synthesis in the brain.

Latency of the dopa reaction in mast cells.

SummaryLight microscopic observations of normal rat peritoneal mast cells and ultrastructural observations of human mast cells from lesions of nodular mastocytosis indicated that structural damage results in a pronounced increase in percentage of cells with a positive dopa reaction. Recent studies have indicated that the dopa reaction in mast cells is peroxidase-dependent. Enhancement of the dopa reaction by structural damage (latency) is probably related to increased substrate-enzyme interaction. Ultrastructural localization of dopa melanin to mast cell granules and the high percentage of mast cells showing a positive dopa reaction after structural damage is evidence against the possibility that dopa melanin is formed in mast cells by phagocytized enzyme.

DOPA compared with dihydroxyfumarate as co-factor in peroxidase-mediated oxidation of tyrosine to melanin

SummaryDihydroxyfumarate was used as a co-factor in the histochemical demonstration of peroxidase-mediated oxidation of tyrosine to melanin in eosinophils, mast cells, melanoma cells and neurons. The use of dihydroxyfumarate as co-factor provides a direct method for demonstrating peroxidase-mediated oxidation of tyrosine to melanin in tissues, and allows for the ultrastructural localization of this pigment.

APPLICATION OF PROTEIN A TO THE STUDY OF PEMPHIGUS ANTIBODIES

FITC‐labeled staphylococcal protein A was used to detect pemphigus antibodies. The results showed that protein A was specific in the systems tested, although it was not as sensitive as FITC‐anti IgG in indirect immunofluorescence tests. Protein A‐adsorbent was used to isolate IgG from pemphigus serum samples. Recovery of pemphigus antibody activity was a mean of 57.1 percent, as high as that of DEAE chromatography. We consider protein A to be an alternative to monospecific anti IgG for detection of pemphigus antibodies and for purification of IgG from pemphigus sera.

Growth Characteristics of a Hamster Cell Line on Collagen Gel

Summary A previously reported (1) hamster monolayer cell culture derived from a fibro-hemangiosarcoma was grown on firm gels of reconstituted collagen. The gel was cleared without concomitant collagenolysis as judged by the release of labeled soluble collagen peptides from the reconstituted gel. In the final phase, the collagen was condensed. Histological examination of the condensed gel revealed a proliferation of cells showing variations in cell appearance within the gel matrix.

A Hamster Fibrohemangiosarcoma: Influence of Host Sex on Tumor Mass

Summary A fibrohemangiosarcoma was produced in hamsters following the injection of cell inocula. These tumors in pregnant, lactating female hamsters attained a wet tumor weight 4-8 times greater than that noted in either adult male or female hamsters within 6-7 wk. Monolayer cell cultures obtained from a fibroma produced by the injection of cells from a Wistar Institute HE-44 culture in its 69th passage was alternately repassaged through inbred Syrian hamsters. Following the fourth animal repassage a culture line was obtained which consistently through the 16th subculture produced tumors composed of spindle cells, endothelial cells and cells intermediate between these two types of cells. It is considered likely that the culture line consisted of mesenchymal cells that have retained some degree of pluripotentiality. Strong acid phosphatase, β-glucuronidase and nonspecific esterase activity was present in the cells of the tumor tissue as well as in the cells grown in culture for 16 passages. It is probable that hormonal influences associated with growth are responsible for the observed differences in wet tumor weight in pregnant and nonpregnant hamsters. This tumor showed histologic resemblance to the human Kaposi sarcoma.

The effect of phospholipids on the lipolytic activity of heparin-induced plasma lipase

Abstract It has been shown that the hydrolysis of triglycerides by heparin-induced plasma lipase can be inhibited by lecithin, cephalin and phosphatidyl serine. The significance of these results was discussed in relation to pancreatic lipase and to the behavior of the heparin-induced lipase in hyperlipemic plasma.