Mitsubishi Petrochemical Company Limited

Masanobu Inagawa

Sachio Hirose

Naoto Miwa

Toshiyuki Sai

Seiichi Kawarabuki

Motomu Hane

There is disclosed a calcitonin derivative and its salt, comprising an amino acid residue at the 1-position of calcitonin which is a cyclic amino acid residue represented by the formula: ##STR1## wherein X represents a sulfur atom or a methylene group; and n represents an integer of 0 or 1. and an amino acid residue at the 7-position which is a cysteine residue which may be substituted with an appropriate protective group.

Novel calcitonin derivative and salt thereof

A method and composition for use therein for measuring the activity of creatine kinase (hereinafter referred to as 'CK') having good storage stability is disclosed. More particularly, a composition for measurement of CK activity which comprises as main components phosphoglycerate kinase (hereinafter referred to a 'PGK') which catalyzes the following reaction 2 and glyceraldehyde-3-phosphate dehydrogenase (hereinafter referred to as 'GAPDH') which catalyzes the following reaction 3. Reaction 1 is catalyzed by the creatine kinase.

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Ibaraki, Japan

Masanobu Inagawa