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THE

REACTION

OF NINHYDRIN

WITH

DIPEPTIDES:

DIFFERENCES

IN

REACTION

RATES

AND

THEORETICAL

YIELDS

(Prom

the

Research

Division,

BY

SAM

YANARI

Armour

and

Company, Chicago,

Illinois)

(Received

for

publication,

July

7,

1955)

Calorimetric

ninhydrin

the violet-colored

product1

methods which

(1, 2) results

are based from the

on the measurement

oxidative

deamination

of

of a primary

amino group by ninhydrin

(1,2,3-indantrione)

at pH values

Theoretical

yields of the

by preventing

oxidative

colored product

are obtained

side

reaction

from

occurring;

higher than 3

(3).

from or-amino

acids

e.g., by

adding

dantin)

(2, 4).

either stannous chloride Since the colored product

(1) or reduced ninhydrin is also formed from th

(hydrin- e primary

amino groups of peptides

(1)) the ninhydrin

method

has been extended to

assay proteins

proteins

(5)

and

as well as

peptides

peptides; (6, 7) and

e.g., chromatographic

fractionation

measurement

of

peptidase

activity

of (8).

Unexpected

was adapted to

peptides.

First

complications

were encountered

when the ninhydrin

measure the enzymatic

hydrolysis

of

all,

several-fold

differences

in

the

of certain

relative

types reaction

assay of di- rates

of two diastereoisomeric

actually

greater

than

dipeptides were observed. those of many structurally

These differences

were

unrelated

dipeptides.

which

affect the reac-

reported

in this paper.

tion

rates

and maximal

color

yields

of dipeptides

are

were

nearly

Furthermore,

the molar

color yields

of certain

twice those of other dipeptides.

Studies on factors

dipeptides

EXPERIMENTAL

Materials-Peptides

were purchased

from the Mann

Research

Labora-

dories, Inc., pany, Ltd.; clantin from B. Hofmann terials were

Hoffmann-La

Roche,

Inc.,

and the H.

M.

Chemical

Com-

ninhydrin from

the Pierce

the Dougherty

Chemicals.

Chemical

Company;

L-Ser-n-Ty?

was a

and hydrin- gift from Dr.

of the University

of Pittsburgh.

No ninhydrin-positive

ma-

detected

by quantitative

paper

chromatography

(10)

when

the

peptides lvould

were examined be detected.3

at levels such that 3 to 4 per cent contamination

Kjeldahl

nitrogen

determinations

and

ultraviolet

r Diketohydrindylidenediketohydrindamine.

dues,

as suggested

by Brand

the

terminal

amino

acid residues

flee

carboxyl

group,

respectively.

2 The

following

abbreviations

and

are used: Edsall of a peptide

peptides,

abbreviation

(9);

N-terminal

and

possessing

t,he free

of amino C-terminal e-amino

acid resi- residues, group and

3 These

studies

were

kindly

carried out

by W. 683

F. White

and

A. M. Gross.

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