Guinea-pig epidermis was irradiated with 3000 rad of beta rays 1 hr after two injections of [3-H]thymidine 5 hr apart (labeled cells in S phase and G2 phase) or 18 hr after injection (labeled early G1 cells). In nonirradiated epidermis labeled basal cells divided within 24 hr with daughter cells remaining in the basal layer, and approximately 50% of the labeled cells moved into the spinal layer by the 3rd day. Cell division in nonirradiated epidermis diluted the number of silver grains/nucleus, and lightly labeled cells were found in the granular layer by day 7. Beta irradiation inhibited cell division but it did not slow the rate of transit (ca 8 days) of irradiated labeled cells from basal to granular layer, some of these remaining heavily labeled. Although cell division may play some role in upward movement of basal cells in normal epidermis detachment of a basal cell from the basement membrane and its transit to the granular layer is unimpaired in the absence of cell division. These findings suggest that some radioresistant metabolic function(s), not cell division, is responsible for upward movement of basal cells.
In a previous paper we reported (21) Peel differ in several respects. This may be due to difference in strain used, or to the fact that our results were based on analysis of cellular suspensions incubated for longer periods of time.
Materials and methodsThe strain of H. anomrala var. longa type B (Naegeli) Dekker, was grown in medium I, TABACHNICK and JOSLYN (21) witlh 1%o of glucose as carbon source. The inedium inoculated with a 107% by volume of a 24-hour growing culture was shaken (7.5 cmu. stroke, 94 cycles per ininute) for 24 hours at room temperature (23 to 26°C). To prevent excess foaming, 0.3 ml. of sterile soy-bean oil was added per liter of shake culture. After harvesting the cells by centrifuging and washing, aseptic technique was no longer observed. Cell nitrogen was determined by the micro-Kjeldahl method.Preliminary experiments showed that, as reported also by PEEL (18), ethanol alone could serve as substrate for ethyl acetate production and that acetate was not necessary. Acetic acid at a concentration of 0.05 I\1 (at pH 3) was toxic. Highest yields of ethyl acetate were obtained in a 20-ml. cell suspension containing 10 ml\I of ethanol, 0.1 'I phosphate buffer at pH of about 3, and at a cell density equivalent to 4.5 to 5.5 mg. of cell nitrogen per 20 ml., shaken in a cotton-stoppered 125-ml. Erlenmeyer flask for 18 to 24 hours at room temperature (23 to 26°C). Unless otherwise stated these conditions were used in subsequent experiments. PEEL (18) reported opti-1 Present address: Northern Division,
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