as, ay,
Table 3. Enzymatic reduction of ketoproline to hydroxyproline. One milliliter of
dialyzed supernatant fraction from a 1:2
KCI homogenate of rat kidney was used.
All of the incubation beakers contained
0.5 ml of 0.544 phosphate buffer, pH 7.4;
1 mg of ketoproline; 5 umole of nicotina-
mide, and 1 ml of rat-kidney preparation
in a final volume of 3 ml. Where indicated, 0.5 umole of DPN, 0.26 ymole of
TPN, 200 pmole of glucose, and 250 units
of glucose dehydrogenase were added.
After 1.5 hours of incubation, hydroxyproline was assayed by a modification of
the Wiss method (2, &).
Hydroxyproline
System
(ug)
DPN + glucose dehydrogenase system
TPN + glucose dehydrogenase system
DPN or TPN withoutglucose dehydrogenase
42.7
52.5
< 3.5
erated in the incubation mixture by the
glucose dehydrogenase system (4), as
shown in Table 3, Reduced TPN (5)
was found to be more active than reduced DPN. The rat-kidney preparation
could not be replaced by purified commercial alcohol or lactic dehydrogenases.
Neither reduced DPN nor reduced TPN
was effective in the absence of the ratkidney preparation.
Theinhibitory effect of ketoproline on
hydroxyproline metabolism is clearly es-
tablished in these studies. The enzyme
responsible for the reduction of ketoproline and the physiological significance of
this reaction are under investigation.
CHozo Miroma, THomas E. SmirH,
Frances M. DaCosta,
Swney UDENFRIEND
National Heart Institute,
National Institutes of Health,
Bethesda, Maryland
ARTHUR A. PATCHETT,
BERNHARD WITKOP
National Institute of Arthritis
and Metabolic Diseases,
National Institutes of Health,
Bethesda, Maryland
References and Notes
~
1. A. A. Patchett and B. Witkop, J. dm. Chem.
Soc. 79, 185 (1957).
2. A report on the modified procedure is in preparation.
R. E. Neuman and M. A. Logan, J. Biol.
Chem, 184, 299 (1950).
4. H. J. Serecker and S. Korkes, ibid. 196, 769
(1952).
5. The following abbreviations are used: DPN,
diphosphopyridine nucleotide; TPN, triphosphopyridine nucleotide.
6. W. Troll and J. Lindsley, J. Biol. Chem, 215,
655 (1955).
7, We are indebted to Dr. R. N. Doetsch of the
University of Maryland for this strain.
8 O. Wiss, Helv, Chim. Acta 32, 149 (1949).
06
Evaporation from
Quiescent Water
Abstract. The color change of a filter
paper impregnated with cobaltous chloride
and held just above the surface of water
gives a good indication of the rate at which
evaporation proceeds from individual regions of the surface. The marked effect of
some monolayers on thermal convection
currents within the liquid can be thus
shown.
The usual technique of measuring the
rate of evaporation of water from a-quiescent surface and the effect of mono-
layers upon this is rather elaborate (!)
yet does not provide any information
about local conditions over small por-
hydroxyproline. This reaction was found
to require the presence of reduced pyridine nucleotides, either as such or gen-
29 August 1958
Direct Observation of
tions of the area studied. This report (2)
presents a few observations based on a
simple technique which gives qualitative
but very direct visual information about
the rate of evaporation and shows what
happensoverareas of the order of a few
square millimeters. The technique is
based on the color change produced by
the vapor reaching a sheet of paper impregnated with cobaltous chloride and
held very close to the surface.
Figure | shows the pattern—which was
actually pink on blue—obtained when
the indicator paper was placed above
a squarecell, 2 by 2 cm,filled with water
whose surface was divided into two parts
by. a polyethylene barrier. To the left of
the barrier the surface was clean, while
some cetyl alcohol was sprinkled over
the surface to the right of the barrier. In
the photograph, taken 2 minutes after
the paper was placed above the surface,
the difference in the rates of evaporation
from the twosides is strikingly apparent.
Over the clean surface the paper is already pink, while over the monolayerit
is still largely blue. In addition, the color
change over the clean surface is uniform
(it developed uniformly from the beginning), while over the protected part the
the indicator paper. Changesin the thermalresistance of the water, reported previously (3), are also in agreement with
this observation.
This change in convection currentsis
connected with the well-known hysteretic
resistance of a monolayer against extensions and contraction (¢). When a cooled
streamline of water detaches itself from
the surface and sinks under the influence
of gravity, the corresponding surface
must shrink. Conversely, when a rising
warm streamline reaches the surfaceit
causes, necessarily, a local expansion of
the surface. When the surface is clean,
such expansions and contractions en-
counter no resistance, but when a mono-
layer is present they are impeded, and
convection at the surface develops only
over greater distances and when larger
forces are present. The heat transport to
the surface from the bulk of the wateris
thus necessarily affected and localized.
In the experiments under discussion
(5), the filter paper was firmly attached
to a glass plate, both to insure an even
surface and to prevent access of vapor
from the back. The plate was first covered with a thin layer of “rubber cement
for pasting paper,” and the filter paper
was firmly pressed onto it. The whole
was then submerged in a moderately concentrated solution of CoCl, (prepared
without heating), excess liquid was
pressed out between filter papers, and the
assembly was dried in a vacuum desic-
cator. The rims of the vessels had to be
coated with paraffin to prevent creeping
of the water. After the rimhad been adjusted to the horizontal, the vessel was
filled with water to within about 1 mm
of the top. The water surface was protected, when protection was desired, by
manualsprinkling of a few specks of commercial cetyl alcohol upon it. A wait of
a few minutes allowed the convection
currents to develop and stabilize. The
glass-backed indicator paper was then
change appears in spots, which gradually
spread over the whole area.
Similar irregular development of the
color, signifying uneven rate of evaporation in the presence of the monolayer,
was observed with a variety of vessels. It
is attributed to the presence of relatively
large convection currents which rise
warm, cause relatively rapid evaporation,
and are thus cooled so that the rate of
evaporation is reduced while they continue along the surface for a distance
before finally sinking. On a clean surface
the convection pattern is different, and
local differences are much smaller. This
interpretation is supported by observation of convection currents made visible
by very slow injection of a very dilute
solution of fluorescein into thesurface.
The convection currents, while irregular,
seem to be more extendedin the presence
of the monolayer, and their general pat-
tern corresponds to that of the spots on
Fig. 1. The local pattern of evaporatiop.,
from a water surface 2 cm square; thevaft
°
side is clean, the right side is protectedby
cetyl alcohol. This photograph of cobaltous chloride indicator paper was taken 2
minutes after the paper was placed above
the water surface.
SCIENCE, VOL. 129